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The UNIX programming environment

1. block device character device directory fifo pipe socket regular normal symbolic link a lock rwx owner read permission write permission group read permission write permission rwx rwx other read permission write permission group grougroup execute search permission 2 file Not POSIX owner owner execute search permission owner A group other other execute search permission other These return true or false when acting on the mode member Here is an example See section readdir example program struct stat statvar stat file amp statvar test return values Lf S_ISDIR statvar st_mode printf Is a directory readdir example program file Cl Dokumente und Einstellungen The UNIX programming environment htm 127 von 198 20 11 2004 11 29 42 The UNIX programming environment The following example program demonstrates the use of the directory functions in dirent and the stat function call OK KK k k k k k kk KK ee HH kk HH KH HH ck k ck ck kk Ck Ck ck kc k ck ck KK k kk x Reading directories and statting files ay ER m ORK KKK KKK KK KK KR ee HH kk kk k kk kok ko kok HH ck ck k ck kc kc kc kc kc k ck KH ck ck include lt stdio h gt include lt dirent h gt finclude lt sys types h gt fincl
2. open all files for everyone chmod 755 set the s bit on my dir s group chmod gts mydir descend recursively into directory opening all files chmod R atr dir Umask When a new file gets created the operating system must decide what default protection bits to set on that file The variable umask decides this umask is normally set by each user in his or her cshrc file see next chapter For example umask 077 safe umask 022 i liberal According the UNIX documentation the value of umask is XOR ed exclusive OR with a value of 666 amp umask for plain files or 777 amp umask for directories in order to find out the standard protection Actually this is not quite true umask only removes bits it never sets bits which were not already set in 666 For instance umask Permission 077 600 plain 077 700 dir 022 644 plain 022 755 dir The correct rule for computing permissions is not XOR but NOT AND Making programs executable file Cl Dokumente und Einstellungen The UNIX programming environment htm 35 von 198 20 11 2004 11 29 42 The UNIX programming environment A unix program is normally executed by typing its pathname If the x execute bit is not set on the file this will generate a Permission denied error This protects the system from interpreting nonsense files as programs To make a program executable for someone you must therefore ensure that they can execute the file using a comm
3. print Content type text htmlXnin Get the data from the form Sinput lt STDIN gt AE and echo them back print input n n n input s g Sinput s g array split amp Sinput file Cl Dokumente und Einstellungen The UNIX programming environment htm 107 von 198 20 11 2004 11 29 42 The UNIX programming environment foreach Svar array print var lt br gt print lt hra n name variablel name variable2 split variablel Sarray 0 split variable2 array 1 print br varl svariablel lt br gt print lt br gt var2 Svariable2 lt br gt print lt br gt Done n and the output variablel Mark Burgess variable2 0D 0AI just called to say wrap 0D 0A heytpigS2Ct nothing 27s tworkingtout thetwaytIt planned variablel Mark Burgess variable2 1 just called to say hey pig nothings working wrap out the way I planned varl Mark Burgess var2 I Just called to say hey pig nothings working out wrap the way I planned Done A complete guestbook example Let us now use this technique to develop a guest book aplication Based on the code above analyze the following code local bin perl Ht HH HERE HEH H EH EH EEE HE EEE HE RE RE ERE RE ERE RE ERE EEE RE EE EE ERE RE ERE RE ERE L ER Guest book Hatt HH HHH HHH EH EH EEE HE EE HE EE EEE EH OEE EH EE OEE HEE EE OE EE OEE OE OE E RE R
4. then echo Warning process would not die try again endif end file Cl Dokumente und Einstellungen The UNIX programming environment htm 60 von 198 20 11 2004 11 29 42 The UNIX programming environment Het HH HHH HE HH EH EH EE RE ERE RE ERE RE EE EHE RE HERE EE HEE CH OEE HE EE OE ERE RE EE RE NER Start from a certain PID Ht HH HHH HEH H EH EH EE EH E ERE ERE RE EHE HERE RE ERE ERE HEE CH EEE HE EE EE EE E EE RE ERE else if S argv then set killarray ps aux awk if 1 user 84 2 gt uid printf Ss 2 user Sargv 1 uid Sargv 2 foreach process S killarray kill 1 process gt dev null kill 15 Sprocess Sleep 2 kill 9 Sprocess gt dev null if kill 9 Sprocess egrep e No such process then echo Warning process would not die try again endif end endif This program would be better written in C or Perl Bourne shell Programmers who are used to C or C often find it easier to program in C shell because there are strong similarities between the two The Bourne shell is somewhat different in style but is structured in a way which makes it better suited to more complicated script writing especially for system administrators Also it is closer to the kernels own exec mechanism The Bourne shell allows subroutines and default values for parameters Most of the system scripts in UNIX are written in the Bourne shell The principles of the Bourne shell are
5. In a large computer community such as a university or even one faculty in a university it is very natural to file Cl Dokumente und Einstellungen The UNIX programming environment htm 161 von 198 20 11 2004 11 29 42 The UNIX programming environment have some kind of system for sharing disks For example there might be a disk server for the staff s home directories a disk server for student s home directories a mail server a software server for SunOS a software server for Ultrix etc One way to achieve this would be to mount every available disk on every machine but this can set up deadlock situations which lead to problems and it is also a waste of resources To set up each workstation on the network we should only have to mount the right disks on the right machines For instance the Sun software server should only be mounted on Sun machines The student disk doesn t have to be mounted on the professor s personal Rolls Royce workstation but everyone needs to mount the mail box area This is a natural task for a script to manage The script would have to check the filesystem table to see that the necessary filesystems were there and if not add them It would also have to mount them It might further be necessary to link the filesystems to some standard locations also a good task for a script There are two ways of mounting NFS filesystems One is to use the normal mount command the other is to to the automounter The a
6. The UNIX programming environment e Interpretation of values in perl e Interrupt handler in sh e lOctlbi e IRC e Iterating over files e Iteration over arrays e Job control e Job numbers in csh e Job moving to background e Joker notation e jpg e jsh e Kernel e kernel e Kernel access e Kernel files e Kernighan and Ritchie C e kill command e ksh ksh e latex e la loader linker e less command e lex e lex e Lexer e libc e libcurses e libm e Library path for C loader e Limitations of shell programs e Links in C e Links where do they point e listen e In s file Cl Dokumente und Einstellungen The UNIX programming environment htm 189 von 198 20 11 2004 11 29 42 The UNIX programming environment e Local variables e Local variables in csh e Local variables in perl e Local variables in sh e locate command e Logging on e Login environment e Login evironment e Long file listing e Long lines continuing e Loops and list separators e Loops in csh e Loops in sh e lp command x e lpg e lpr command e lpstat e ls l e ls command e l1stat e MacIntosh e Macros for stat e Mail clients e make e Make rules for C e Make software script e Making a script e Making directories e Making scripts in sh e Masking programs executable e Matching filenames Matching filenames e Matching strings e mc e Me
7. This example replaces the string inside the default variable To replace in a general variable we use the operator with syntax Svariable s search replace Here is an example of some of this operator in use The following is a program which searches and replaces a string in several files This is useful program indeed for making a change globally in a group of files The program is called file replace local bin perl HEH Ht HH HH HH HH EE HE HH HH EH HH HH EE EE EH HH HH EEE EE HE EH EEE EEE EE 25 Look through files for findstring and change to newstring in all files HEH HT HH HH HH HH EE HE HH EH HH HEE EE EH HH HH EEE EH EE EH EEE OE EE EE Define a temporary file and check it doesn t exist Soutputfile tmpmarkfind unlink Soutputfile Check command line for list of files if S ARGV lt 0 die Syntax file replace file list n print Enter the string you want to find Don t use quotes n n Sfindstring lt STDIN gt chop Sfindstring file Cl Dokumente und Einstellungen The UNIX programming environment htm 93 von 198 20 11 2004 11 29 42 The UNIX programming environment print Enter the string you want to replace with Apes Sreplacestring lt STDIN gt chop Sreplacestring print nFind findstring n print Replace replacestring n print nConfirm y n 5 Sy lt STDIN gt chop y if Sy ne y die Aborted nothing done
8. e Sys e users e usr e usr bin e usr local e var e var adm e vr spool e mg Be file Cl Dokumente und Einstellungen The UNIX programming environment htm 174 von 198 20 11 2004 11 29 42 The UNIX programming environment e lt lt less than e lt lt lt lt e lt lt shift e lt e assignment e insh e set E e equal to compare e gt e gt e gt e gt greater than e gt e gt gt e gt gt shift e e inregular expressions e e in regular expressions e inregular expressions e XOR file Cl Dokumente und Einstellungen The UNIX programming environment htm 175 von 198 20 11 2004 11 29 42 The UNIX programming environment a e apropos e ar e archie e argcinC e argv in C e awk e breaksw C e cat e e e cc e chgrp e chmod e chown e cmdtool e continue e date e dbx e dc e ddd e df e DISPLAY e domainname e du file Cl Dokumente und Einstellungen The UNIX programming environment htm 176 von 198 20 11 2004 11 29 42 The UNIX programming environment e dvips e find e finger e fmgr e _fnews e foreach e fork e ftp e g e acc e qgdb e getenv e ghostscript e ghostview e HOME e HOST e hostname e 10ctl e irc e ispell file Cl Dokume
9. lt CENTER gt lt H2 gt Please leave a comment using the form below lt H2 gt lt P gt lt FORM method POST ACTION cgi bin mark comment pl gt Your Name e mail lt INPUT NAME variablel SIZE 40 lt BR gt lt BR gt lt P gt lt TEXTAREA NAME variable2 cols 50 rows 8 gt lt TEXTAREA gt lt P gt lt INPUT TYPE submit VALUE Add message to book gt lt INPUT TYPE reset VALUE Clear message gt lt FORM gt lt P gt file Cl Dokumente und Einstellungen The UNIX programming environment htm 104 von 198 20 11 2004 11 29 42 The UNIX programming environment BODY lt HTML gt The reset button clears the form When the submit button is pressed the CGI program is activated Interpreting data from forms To interpret and respond to the data in a form we must write a program which satsifies the protocol above See section Protocols We use perl as a script langauge The simplest valid CGI script is the following local bin perl Reply with proper protocol print Content type text html n n Get the data from the form Sinput lt STDIN gt E and echo them back print input An Done n Although rather banal this script is a useful starting point for CGI programming because it shows you just how the input arrives at the script from the HTML form The data arrive all in a single enormously long line full of funny characters The first job of any script
10. search string Here teststring is searched for occurrances of search string and the result is true if one is found file Cl Dokumente und Einstellungen The UNIX programming environment htm 95 von 198 20 11 2004 11 29 42 The UNIX programming environment In perl you can use regular expressions to search for text patterns Note however that like all regular expression dialects perl has its own conventions For example the dollar sign does not mean match the end of line in perl instead one uses the n symbol Here is an example program which illustrates the use of regular expressions in perl local bin perl Test regular expressions in perl NB careful with symbols etc Use quotes since the shell interprets these open FILE regex test Sregex SARGV S ARGV print Looking for SARGV S ARGV in file n while lt FILE gt if regex print Test like this regex prints every line matches everything regex all lines except those containing only blanks doesn t match ws white space regex a z matches any line containing lowercase regex a z matches any line containg something which is not lowercase a z regex A Za z matches any line containing letters of any kind regex 0 9 match any line containing numbers regex line containing a hash symbol followed by anything regex
11. Notice that each element in an array is a scalar variable The cannot be interpreted directly as the number of elements in the array as it can in the C shell You should experiment with the value of this quantity it often necessary to add 1 or 2 to its value in order to get the behaviour one is used to in the C shell Perl does not support multiple dimension arrays directly but it is possible to simulate them yourself See the Perl book Special array commands The shift command acts on arrays and returns and removes the first element of the array Afterwards all of the elements are shifted down one place So one way to read the elements of an array in order is to repeatedly call snift Snext_element shift myarray file Cl Dokumente und Einstellungen The UNIX programming environment htm 78 von 198 20 11 2004 11 29 42 The UNIX programming environment Note that if the array argument is omitted then shift works on ARGV by default Another useful function is split which takes a string and turns it into an array of strings split works by choosing a character usually a space to delimit the array elements so a string containing a sentence separated by spaces would be turned into an array of words The syntax is array split works with spaces on S_ array split pattern string Breaks on pattern Svl1 v2 split pattern string 4 Name array elements with scalars In the first
12. Suffix rules C o CCPLUS c lt The general rule here tells make thata o file can be created from a c file by executing the command CCPLUS c This is identical to the C case exept for the name of the compiler The extra dependencies tell make that if we change the header file filesys h then we must recompile all the files which read in ilesys nh since this could affect all of these Finally the highest level rule says that to make ilesys from the o files we have to run S CCPLUS o filesys o argv argc and envp When we write a C program which is to read command line arguments they are fed to us as an array of strings called the argument vector The mechanisms for the C shell and Perl are derived from the C argument vector To read in the command line we write main argc argv envp int argc file Cl Dokumente und Einstellungen The UNIX programming environment htm 121 von 198 20 11 2004 11 29 42 The UNIX programming environment char argv envp l printf The first argument was s n argv 1 Argument zero is the name of the program itself and argv argc 1 is the last argument The above definitions are in Kernighan and Ritchie C style In ANSI C the arguments can be declared using prototype main int argc char argv The array of strings envp is a list of values of the environment variables of the system formatted by NAME value Th
13. d or 1 The next three bits set the so called s bits and t bit which are explained below The remaining three groups of three bits set flags which indicate whether a file can be read r written to w or executed x by i the user who created them ii the other users who are in the group the file is marked with and iii any user at all For example the permission Type Owner Group Anyone d rwx r x tells us that the file is a directory which can be read and written to by the owner can be read by others in its group but not by anyone else Note about directories It is impossible to cd to a directory unless the x bit is set That is directories must be executable in order to be accessible Here are some examples of the relationship between binary octal and the textual representation of file modes Binary Octal Text 001 1 x 010 2 W 100 4 a 110 6 rw 101 5 r x 644 rw r r It is well worth becoming familiar with the octal number representation of these permissions file Cl Dokumente und Einstellungen The UNIX programming environment htm 34 von 198 20 11 2004 11 29 42 The UNIX programming environment chmod The chmod command changes the permission or mode of a file Only the owner of the file or the superuser can change the permission Here are some examples of its use Try them make read write able for everyone chmod atw myfile add the execute flag for directory chmod u x mydir
14. file Cl Dokumente und Einstellungen The UNIX programming environment htm 4 von 198 20 11 2004 11 29 41 The UNIX programming environment complete To use this programming guide you will need to work through the basics from each chapter You will find that there is much more information here than you need straight away so try not to be overwhelmed by the amount of material Use the contents and the indices at the back to find the information you need If you are following a one semester UNIX course you should probably concentrate on the following The remainder of this introduction The detailed knowledge of the C shell An appreciation of the Bourne shell A detailed knowledge of Perl guided by chapter 6 This chapter provides pointers on how to get started in perl It is not a substitute for the perl book e Everything in chapter 7 about C programming This chapter is written in note form since it is assumed that you know a lot about C programming already e A sound appreciation of chapter 8 on network programming The only way to learn UNIX is to sit down and try it As with any new thing it is a pain to get started but once you are started you will probably come to agree that UNIX contains a wealth of possibilities perhaps more than you had ever though was possible or useful One of the advantages of the UNIX system is that the entire UNIX manual is available on line You should get used to looking for information in the on
15. fprintf stderr This is an error message n The names are logical in the sense that they do not refer to a particular device or a particular place for information to come from or go Their role is analogous to the and directories in the filesystem Programs can write to these files without worrying about where the information comes from or goes to The user can personally define these places by redirecting standard I O This is discussed in the next chapter file Cl Dokumente und Einstellungen The UNIX programming environment htm 8 von 198 20 11 2004 11 29 41 The UNIX programming environment A separate stream is kept for error messages so that error output does not get mixed up with a program s intended output The superuser root and nobody When logged onto a UNIX system directly the user whose name is root has unlimited access to the files on the system root can also become any other user without having to give a password root is reserved for the system administrator or trusted users Certain commands are forbidden to normal users For example a regular user should not be able to halt the system or change the ownership of files see next paragraph These things are reserved for the root or superuser In a networked environment root has no automatic authority on remote machines This is to prevent the system administrator of one machine in Canada from being able to edit files on another in China He or she
16. mode Soctalmode n file Cl Dokumente und Einstellungen The UNIX programming environment htm 80 von 198 20 11 2004 11 29 42 The UNIX programming environment print In order LEAST secure first n n foreach i reverse sort keys assoc_array print assoc array S i Loops and conditionals Here are some of the most commonly used decision making constructions and loops in Perl The following is not a comprehensive list for that you will have to look in the Perl bible Programming Perl by Larry Wall and Randal Schwartz The basic pattern follows the C programming language quite closely In the case of the or loop Perl has both the C like version called for and a foreach command which is like the C shell implementation if expression block else block command if expression unless expression block else block while expression block do block while expression for initializer expression statement file Cl Dokumente und Einstellungen The UNIX programming environment htm 81 von 198 20 11 2004 11 29 42 The UNIX programming environment block foreach variable array block In all cases the e1se clauses may be omitted Strangely perl does not have a switch statement but the Perl book describes how to make one using the features provided The for loop The for loop is exactl
17. using the telnet or rlogin programs If you use these programs you will normally only get a text or command line interface though graphics can still be arranged Once you have logged in a short message will be printed called Message of the Day or motd and you will see the C shell prompt the name of the host you are logged onto followed by a percent sign e g file Cl Dokumente und Einstellungen The UNIX programming environment htm 11 von 198 20 11 2004 11 29 41 The UNIX programming environment SunOS Release 5 5 Version Generic UNIX R System V Release 4 0 Copyright Ic 1983 1995 Sun Microsystems Inc Please report problems to sysadm iu hioslo no dax Remember that every unix machine is a separate entity it is not like logging onto a PC system where you log onto the network i e the PC file server Every unix machine is a server The network in unix land has lots of players The first thing you should do once you have logged on is to set a reliable password A poor password might be okay on a PC which is not attached to a large network but once you are attached to the internet you have to remember that the whole world will be trying to crack your password Don t think that no one will bother some people really have nothing better to do A password should not contain any word that could be in a list of words in any language or be a simple concatenation of a word and a number e g mark123 It takes seconds to cr
18. 153 von 198 20 11 2004 11 29 42 The UNIX programming environment In the ULTRIX operating system a configuration file etc svc conf allows the system administrator to decide where gethostbyname will search for data It can for example be told to look first in the DNS database then in NIS and then in etc hosts on the local host Under SunOS the default is to first look in NIS and then provided a special option is compiled into the NIS maps it will continue to search in DNS A replacement library package is available freely called resolv This package is also used on Linux systems It enables the behaviour to be configured independently of how NIS is configured The order for interrogating the databases is held in a file etc host conf which contains a line of the form order hosts bind nis In the solaris operating system the file nsswitch conf is used to control the order of lookups The file etc resolv conf can also contain this kind of information in later releases of the BIND software but this 1s often ignored or overridden by the mechanisms mentioned above nslookup The user level command nslookup can be used to query the nameserver The syntax is nslookup host domain nslookup IPaddress For example nexus nslookup ftp uu net Server elektron uio no Address 129 240 22 222 Non authoritative answer Name ftp uu net Address 192 48 96 9 nexus nslookup 129 240 22 224 Server elektron uio no Addre
19. A commerical mail package tkrat file Cl Dokumente und Einstellungen The UNIX programming environment htm 25 von 198 20 11 2004 11 29 42 The UNIX programming environment A graphical mail reader which supports most MIME types written in tcl tk This program has a nice feel and allows you to create a searchable database of old mail messages but has a hopeless locking mechanism File transfer ftp The File Transfer program copies files to from a remote host ncftp An enhanced ftp for anonymous login Compilers CC The C compiler DE The C compiler gcc The GNU C compiler g The GNU C compiler ld The system linker loader ar Archive library builder dbx A symbolic debugger gdb The GNU symbolic debugger xxgdb The GNU debugger with a windown driven front end ddd A motif based front end to the gdb debugger Other interpreted languages perl Practical extraction an report language tol A perl like language with special support for building user interfaces and command shells scheme A lisp like extensible scripting language from GNU mercury A prolog like language for artificial intelligence Processes and system statistics file Cl Dokumente und Einstellungen The UNIX programming environment htm 26 von 198 20 11 2004 11 29 42 The UNIX programming environment ps List system process table vmstat List kernel virtual memory statistics netstat List network connections and statistics rp
20. SIGCHLD SIGCLD to parent on child stop or exit 21 SIGITIN to readers pgrp upon background tty read 22 SIGTTOU like TTIN for output if tp gt t local amp LTOSTOP 23 SIGIO SIGPOLL input output possible signal 24 STGXCPU exceeded CPU time limit 25 SIGXFSZ exceeded file size limit 26 SIGVTALRM virtual time alarm 21 amp SIGPROE profiling time alarm 28 SIGWINCH window changed 29 SIGLOST resource lost eg record lock lost 30 SIGUSRI user defined signal 1 31 SIGUSBA We have already mentioned 15 and 9 which are the main signals for users Signal 1 or HUP can be sent to certain programs by the superuser For instance k ll 1 lt inetd gt kill HUP lt inetd gt which forces inetd to reread its configuration file Sometimes it is useful to suspend a process temporarily and then restart it later kill 18 lt PID gt suspend process lt PID gt kill 19 lt PID gt resume process lt PID gt Child Processes and zombies When you start a process from a shell regardless of whether it is a background process or a foreground process the new process becomes a child of the original shell Remember that the shell is just a unix process itself Moreover if one of the children starts a new process then it will be a child of the child a grandchild Processes therefore form hierachies Several children can have a com
21. The commands unset and unsetenv can be used to undefine or delete variables when you don t want them anymore Arrays A useful facility in the C shell is the ability to make arrays out of strings and other variables The round parentheses do this For example look at the following commands nexus set array abcd nexus echo Sarray 1 a nexus echo Sarray 2 b nexus echo arrayl array d nexus set noarray a bcd nexus echo Snoarray 1 file Cl Dokumente und Einstellungen The UNIX programming environment htm 39 von 198 20 11 2004 11 29 42 The UNIX programming environment abcd nexus echo S noarray noarray abcd The first command defines an array containing the elements a b c d The elements of the array are referred to using square brackets and the first element is Sarray 1 The last element is array 4 NOTE this is not the same as in C or C where the first element of the array is the zeroth element The special operator returns the number of elements in an array This gives us a simple way of finding the end of the array For example nexus echo S path 23 nexus echo The last element in path is Spath S path The last element in path is To find the next last element we need to be able to do arithmetic We ll come back to this later Pipes and redirection in csh The symbols have a special meaning in the shell By default most commands
22. This means that we can plan out a strategy for writing large programs in a clear and efficient manner You should also format your source code following careful guidelines such as those suggested in the style guide NOTE C style comments are not allowed by most C compilers Macros and declarations Most UNIX systems now have ANSI C compatible compilers but this has not always been the situation Also most UNIX programs written in a version of C which is older than the ANSI standard so you will need an appreciation of old Kernighan and Ritchie C conventions for C programming See for example my C book An obvious difference between ANSI C and K amp R C is that the C additions to the language are not included Here are some useful points to remember e K amp R C does not allow const data it uses the C preprocessor with define instead i e intead of const int blah 1 use define blah 1 Remember that the hash symbol must be the first character on a line under UNIX e K amp R C doesn t use function prototypes or declarations of the form void function char string int a int b Instead one writes file Cl Dokumente und Einstellungen The UNIX programming environment htm 112 von 198 20 11 2004 11 29 42 The UNIX programming environment void function string a b char string int a b Several files Most unix programs are very large and are split up into many files Remember
23. collapse several shell windows into a single xterm window by running the program screen The screen command allows you to start several shells in a single window using CTRL a CTRL c and to switch between them by typing CTRL a CTRL n It is only possible to see one shell window at a time but it is still possible to cut and paste between windows and one has a considerable saving of space The screen command also allows you to suspend a shell session log out log in again later and resume the session precisely where you left off Here is a summary of some useful screen commands Screen Start the screen server screen r Resume a previously suspended screen session if possible CTRL a CTRL c Start a new shell on top of the others a fresh screen in the current window CTRL a CTRL n Switch to the next screen CTRL a CTRL a file Cl Dokumente und Einstellungen The UNIX programming environment htm 32 von 198 20 11 2004 11 29 42 The UNIX programming environment Switch to the last screen used CTRL a a When screen is running CTRL a is used for screen commands and cannot therefore be used in its usual shell meaning of jump to start of line CTRL a a replaces this CTRL a CTRL d Detach the screen session from the current window so that it can be resumed later It can be resumed with the screen r command CTRL a Help screen Files and access To prevent all users from being able to access all files on the
24. commands used solely by the system administrator from user commands and so that they lie on the system root partition where they are guaranteed to be accessible during booting file Cl Dokumente und Einstellungen The UNIX programming environment htm 9 von 198 20 11 2004 11 29 41 The UNIX programming environment sys This holds the configuration data which go to build the system kernel See below export Network servers only use this This contains the disk space set aside for client machines which do not have their own disks It is like a virtual disk for diskless clients dev devices A place where all the logical devices are collected These are called device nodes in unix and are created by mknod Logical devices are UNIX s official entry points for writing to devices For instance dev console is a route to the system console while dev kmem is a route for reading kernel memory Device nodes enable devices to be treated as though they were files home Called users on some systems Each user has a separate login directory where files can be kept These are normally stored under home by some convention decided by the system administrator ar System 5 and mixed systems have a separate directory for spooling Under old BSD systems usr spool contains spool queues and system data var spool and var adm etc are used for holding queues and system log files vmunix This is the program code for th
25. sed search and replace file Cl Dokumente und Einstellungen The UNIX programming environment htm 193 von 198 20 11 2004 11 29 42 The UNIX programming environment e Send e Sending messages e Set command e setenv command e setgid bit e Setting the prompt e Setting up the C shell e Setting up the x environment e setuid bit e SetUID scripts e sh e sh e sh5 e Shared libraries e Sharing filesystems e shell shell shell e Shell commands and C library calls e Shells various e shelltool e shift and arrays e shift and arrays in perl e shift operator on strings e showmount e shutdown command e Signal handler in sh e Single and double quotes e sleep command e Socket e Sockets e Soft links e Sonar ping e Spelling checker e split and arrays e split command e Splitting C into many files e Splitting output to several files e Standard error e Standard I O in perl e Standard I O in sh e Standard I O redirection e Standard input e Standard output e Starting e Starting shell jobs file Cl Dokumente und Einstellungen The UNIX programming environment htm 194 von 198 20 11 2004 11 29 42 The UNIX programming environment e Stat e Static linking e Statistics about a file e Sticky bit e Strings in perl e stty and switching off term echo e Subroutines in perl e Subshells and e Suffix rules in Makefil
26. virtual memory stats file Cl Dokumente und Einstellungen The UNIX programming environment htm 196 von 198 20 11 2004 11 29 42 The UNIX programming environment Ww e w command e wait h e Waiting for child processes e whereis command e Which command e while e while in perl e while in sh e while loop in sh e who command e whoami command e Wildcards Wildcards e Windows on PC e Wrapper functions e Wrappers e write command e write example e Writing a script e WIERMSTG status e X access control e X display X display e X protocol e X window system e X windows e X windows access e X windows authentification e X windows e xarchie client e Xauthority mechanism e xedit e xemacs x e xfig drawing program e xhost mechanism e _xpaint program e xrn news reader e xterm e xterm program e xvV picture processor file Cl Dokumente und Einstellungen The UNIX programming environment htm 197 von 198 20 11 2004 11 29 42 The UNIX programming environment e xxgdb e yacc e udsco yaco e zmail client e zsh symbol symbol This document was generated on 24 June 1997 using the texi2html translator version 1 50 file Cl Dokumente und Einstellungen The UNIX programming environment htm 198 von 198 20 11 2004 11 29 42
27. when you split up programs into several files you must declare variables as extern in file A if they are really declared in file B in which you want to use them This tells the compiler that it should not try to create local storage for the variable because this was already done in another file A note about UNIX system calls and standards Most of the system calls in UNIX return data in the form of struct variables Sometimes these are structures used by the operating system itself in other cases they are just put together so that programmers can handle a packet of data in a convenient way If in doubt you can find the definitions of these structures in the relevant include files under usr include Since UNIX comes in many flavours the system calls are not always compatible and may have different options and arguments Because of this there is a number of standardizing organizations for UNIX One of them is POSIX which is an organization run by the major UNIX vendors Programs written for UNIX are now expected to be POSIX compliant This is not something you need to think about at the level of this course but you should certainly remember that there exist programming standards and that these should be adhered to The aim is to work towards a single standard UNIX Compiling cc 1d and a out The C compiler on the unix system is traditionally called cc and has always been traditional part of every unix environme
28. 11 2004 11 29 42 The UNIX programming environment fe ey if strcmp x y 0 Opening a file C shell Bourne shell cannot be done pipes only Perl open READ HANDLE filename open WRITE HANDLE filename open APPEND_HANDLE gt gt filename UE WE FILE fp fp fopen file r E fp fopen rfile w s fp fopen file a Opening a directory C shell foreach dir directory end Bourne shell for dir in directory j do done Perl opendir HANDLE directory die while Sentry readdir HANDLE file Cl Dokumente und Einstellungen The UNIX programming environment htm 170 von 198 20 11 2004 11 29 42 The UNIX programming environment closedir HANDLE include lt dirent h gt DIR dirh Struct dirent dirps if dirh opendir name NULL perror opendir exit 1 for dirp readdir dirh dirp NULL dirp readdir dirh dirp d name points to child closedir dirh Testing file types C shell if f file plain file if d file directory i Bourne shell if f file plain file if ed file directory Perl if f file plain file if d file directory if 1 file symbolic link LEE RT include lt sys stat h gt struct stat statvar file Cl Dokumente und Einstellungen The UNIX programming environment htm 171 von 198 20 11 2004 11 29 42 Th
29. 180 von 198 20 11 2004 11 29 42 The UNIX programming environment program sequence program sequence e in regular expressions e operator e and e and subshells e operators to make array in csh e in regular expressions e in regular expressions e I option to cc e L option to cc directory directory e in regular expressions directory directory e cshrc file login file e profile setupin sh xsession file Jetc fstab file Cl Dokumente und Einstellungen The UNIX programming environment htm 181 von 198 20 11 2004 11 29 42 The UNIX programming environment etc group etc group fjetc passwd e l insh e 2 insh e 2 amp l insh e lt gt filehandle in perl e inregular expressions e for test in sh e in regular expressions e in regular expressions e symbol and embedded shells e t in perl e a out e accept e Access bits e Access bits octal form e Access bits text form e Access control file Cl Dokumente und Einstellungen The UNIX programming environment htm 182 von 198 20 11 2004 11 29 42 The UNIX programming environment e Access control lists e Access rights e Access to files e ACLs e ANSIC e Appending to a file with e apropos e ar archiver e _archie program e Argument vector in csh e Argument vector in perl Argument v
30. J Levine T Mason and D Brown O Reilly and Assoc 51 OK KKK k k HH X k kk k k k ee oko kok ok X X X ck ck ck ck ck ck kc k ck ck ckck ck ck ckckck ck kk 7 PARSER for a b protocol al 22 The section between the single s gets copied verbatim into ur the resulting C code yacc generates including this comment A s KKK K KKK kk kk K AKA X XK AAA X XK AA X XK AA AX X XK AA X KAZ HH X ck ckck kc kck ck kc kckck ck ck kk include lt stdio h gt extern char yytext oo token NUMBER PLUS file Cl Dokumente und Einstellungen The UNIX programming environment htm 123 von 198 20 11 2004 11 29 42 The UNIX programming environment oe oe Specification yyerror Warning invalid statement statement statement NUMBER PLUS NUMBER The lexer to go with this parser generates the tokens NUMBER and PLUS used by yacc 7 uM DUM a PLINIUM Uu LI DUM du dL E Le n LEXER for a b protocol 7 Returns token types NUMBER and PLUS to yacc one at a time ay iod ua OR KK k k kk HH X k kk HK HH HH ck ck ck k ck Ck Ck ck ck kck ck KK KK include y tab h yacc produces this need this line 5 number O 9 plus number return NUMBER plus return PLUS return yytext 0 oe oe EOF The main program which uses yacc and 1ex looks like this extern FILE yyin file Cl Dokumente und Einstellungen The U
31. System administration can be automated to a large extent by writing scripts and or programs in C Moreover UNIX already contains a lot of scripts which are written in the shell By means of examples and for inspiration let us touch briefly on some of the system configuration issues Booting and shutting down the system file Cl Dokumente und Einstellungen The UNIX programming environment htm 157 von 198 20 11 2004 11 29 42 The UNIX programming environment The most important time the system has to be configured is when it starts up The boot procedure Normally a UNIX machine will try to boot when it is switched on On some systems it might be necessary to type b or boot Each system has its own conventions A system boots by executing the boot block on the first partition of disk number zero The boot block is like a signal which tells UNIX that the machine is allowed to boot from that partition If a disk has no boot block the machine will not boot from it On a BSD system the boot block simply mounts the first roo partition and loads the boo program under ULTRIX this file is called ultrixboot which subsequently loads the kernel file vmunix On the HPUX system the kernel is loaded by the initial system loader and is called hp ux Newer systems have other names for the kernel The last step of the boot procedure is to start the process called init which starts by running some configuration scripts an
32. access semion root semion export swapl semion access semion root semion mn anyon local access local hosts external machine dom com Note you should always check the manual on your machine because there is always something which is different on a different implementation of UNIX The access command gives permission to the hosts boson fermion semion and anyon The root account on fermion and boson has no privileges in the filesystem usr on the server root gets mapped to the user nobody as usual But the command root boson on the next line means that the machine boson can write to the filesystem export root boson with all privileges This is used to allow diskless machines to to use a disk on a remote server for example A final note about the last line is in order The entry local hosts stands for a whole group of names It is called a netgroup We only note that the possibility exists for keeping the file tidy using collective names On the ULTRIX system we only need to edit the file etc exports This file is reread on each mount request On most systems the export list is cached in memory and it is necessary to update this cache file Cl Dokumente und Einstellungen The UNIX programming environment htm 163 von 198 20 11 2004 11 29 42 The UNIX programming environment by running the program exportfs a This only works if the NFS server daemons are running Under solaris 2 the export mechanism has
33. also read such lists directly See section Loops in sh A Perl script can also be used The value of a variable is given by the dollar symbol as in C shell It is also possible to use curly braces around the variable name to protect the variable from interfering text For example animal worm S echo bookSanimal bookworm S thing book echo Sthingworm nothing echo thing worm bookworm Default values can be given to variables in the Bourne shell The following commands illustrate this echo S var No value set echo S var Octopus echo S var Forced value file Cl Dokumente und Einstellungen The UNIX programming environment htm 62 von 198 20 11 2004 11 29 42 The UNIX programming environment echo S var No such variable The first of these prints out the contents of var if it is defined If it is not defined the variable is substituted for the string No value set The value of var is not changed by this operation It is only for convenience The second command has the same effect as the first but here the value of var is actually changed to Octopus if var is not set The third version is slightly peculiar If var is already set its value will be forced to be Forced value otherwise it is left undefined Finally the last instance issues an error message No such variable if var is not defined Stdin stdout and stderr In the Bourne shell the standard input output files are re
34. are applied to solve day to day problems The result is either a mess which works somehow like UNIX or a blank refusal to change like DOS or Maclntosh From a practical perspective Unix is important and successful because it is a multi process system which e has an enormous functionality built in and the capacity to adapt itself to changing technologies is relatively portable is good at sharing resources but not so good at security has tools which are each developed to do one thing well allows these tools to be combined in every imaginable way using pipes and channeling of data streams e incorporates networking almost trivially because all the right mechanisms are already there for providing services and sharing building client server pairs etc e itis very adaptable and is often used to develop new ideas because of the rich variety of tools it possesses Unix has some problems it is old it contains a lot of rubbish which no one ever bothered to throw away Although it develops quickly at light speed compared to either DOS or Macintosh the user interface has been the slowest thing to change Unix is not user friendly for beginners it is user friendly for advanced users it is made for users who know about computing It sometimes makes simple things difficult but above all it makes things possible The aim of this introduction is to e introduce the unix system basics and user interface e develop the unix philosoph
35. at the following program local bin perl Nothing file Cl Dokumente und Einstellungen The UNIX programming environment htm 76 von 198 20 11 2004 11 29 42 The UNIX programming environment print Nothing nothing n print Nothing is zero n if nothing 0 if Snothing eq print STDERR Nothing is really nothing n Snothing 0 print Nothing is now nothing n The output from this program is Nothing Nothing is zero Nothing is really nothing Nothing is now 0 There are several important things to note here First of all we never declare the variable nothing When we try to write its value perl creates the name and associates a NULL value to it i e the empty string There is no error Perl knows it is a variable because of the symbol in front of it All scalar variables are identified by using the dollar symbol Next we compare the value of nothing to the integer 0 using the integer comparison symbol and then we compare it to the empty string using the string comparison symbol eq Both tests are true That means that the empty string is interpreted as having a numerical value of zero In fact any string which does not form a valid integer number has a numerical value of zero Finally we can set nothing explicitly to a valid integer string zero which would now pass the first test but fail the second As extra spice this program also demonstrat
36. been replaced by the share command The file etc exports no longer exists but is replaced by a shell script etc d s dfstab which executes a number of share commands In addition a script shareall is provided which does the equivalent of exportis a Passwords groups and netgroups Another place for scripts and utility programs is for user registration Remarkably there are no particularly good programs bundled with any machines for performing this task realistically If a network has only one or two users the password file could be edited directly but consider the start of semester at a university when maybe hundreds of students need accounts in one go All we have is their names but we need to think of usernames and passwords for them create directories and give them appropriate privileges so that they can only log in on student machines This is an ideal task for a script DNS BIND etc resolv conf and etc host conf etc Each host needs to have a list of nameservers for resolving internet domain names On each system the information about where to find a server for the name service is contained in the file etc resolv conf The basic format of this file is as follows domain iu hioslo no nameserver 128 39 89 10 nameserver 129 240 22 230 nameserver 129 240 2 3 This file is empty on a new machine but its presence is crucial if the system is to be able to communicate on the internet The first line declare
37. being run on by calling uname Then it defines a variable MAKE which contains the path to the make program which will build software The make program reads a file file Cl Dokumente und Einstellungen The UNIX programming environment htm 53 von 198 20 11 2004 11 29 42 The UNIX programming environment called Makefile which contains instructions for compiling the program but this file needs to know the type of UNIX so the script first copies a file Makefile src using sed replace a dummy string with the real name of the UNIX Then it calls make and sets the correct permission on the file using chmod bin csh f HGH HE HH HH HE EH EH HH EE EEE EEE EH HE EE EH HH EH HE EE EE EHH CONFIGURE Makefile AND BUILD software HEE HE HH HH HE EH EH HH TEA AE EEE EEE EH HHH EE EE HH HE HE EE EHEHEH set NAME uname r s switch SNAME 1 case SunOS switch SNAME 2 case 4 setenv TYPE SUN4 setenv MAKE bin make breaksw case 5 setenv TYPE SOLARIS setenv MAKE usr ccs bin make breaksw endsw breaksw case ULTRIX setenv TYPE ULTRIX setenv MAKE bin make breaksw case HP UX setenv TYPE HPuUX setenv MAKE bin make breaksw case AIX setenv TYPE AIX setenv MAKE bin make breaksw case OSF setenv TYPE OSF setenv MAKE bin make file Cl Dokumente und Einstellungen The UNIX programming environment htm 54 von 198 20 11 2004 11 29 42 The UNIX programming
38. done echo HELP This very simple script is a typical use for a while loop It gets text repeatedly until the user type quit Since read never returns false unless an error occurs or it detects an EOF end of file character CTRL D it will never exit without some help from an if test If it does receive a CTRL D signal the script prints HELP bin sh Watch in the background for a particular user and give alarm if he she logs in To be run in the background using amp if S ne 1 then echo Give the name of the user as an argument dev tty exit 1 fi echo Looking for SL until users grep s 91 do sleep 60 done echo WAKE UP dev tty echo User 1 just logged in dev tty This script uses grep in silent mode s option i e grep never writes anything to the terminal The only thing we are interested in is the return code the piped command produces If grep detects a line containing the username we are interested in then the result evaluates to TRUE and the sleep loop exits Our final example is the kind of script which is useful for a system administrator It transfers over the Network Information Service database files so that a slave server is up to date All we have to do is make a list of the files and place itin a or loop The names used below are the actual names of the NIS maps well known to system administrators bin sh file Cl Dok
39. exactly where you were You now choose very long filename by typing 1 This is enough to uniquely identify the file Pressing the TAB key again results in more very long filename on the screen As long as you have written enough to select a file uniquely the shell will be able to complete the name for you Completion also works on shell commands but it is a little slower since the shell must serach through all the directories in the command path to complete commands Single and double quotes Two kinds of quotes can be used in shell apart from the backward quotes we mentioned above The essential difference between them is that certain shell commands work inside double quotes but not inside single quotes For example file Cl Dokumente und Einstellungen The UNIX programming environment htm 44 von 198 20 11 2004 11 29 42 The UNIX programming environment nexus echo etc rc etc rc boot etc rc ip etc rc local nexus echo etc rc etc ro nexus echo who am i my name is user nexus mark ttyp Jul 13 10 16 my name is mark nexus echo who am i my name is user who am i my name is user We see that the single quotes prevent variable substitution and sub shells Wildcards do not work inside either single or double quotes N Job control break key q bg So far we haven t mentioned UNIX s ability to multitask In the Bourne shell sn there are no facilities f
40. file Cl Dokumente und Einstellungen The UNIX programming environment htm 110 von 198 20 11 2004 11 29 42 The UNIX programming environment Burgess lt a gt Mark Burgess iu hioslo no lt addre ss lt html gt Try to work through this example step for step C programming This section is not meant to teach you C It is a guide to using C in UNIX and it is assumed that you have a working knowledge of the language Shell or C In the preceding chapters we have been looking at ways to get simple programming tasks done The immediateness of the script languages is a great advantage when we just want to get a job done as quickly as possible Scripts lend themselves to simple system administration tasks like file processing but they do not easily lend themselves to more serious programs Although some system administrators have grown to the idea that shell programming is easier would argue that this is not really true First of all most of the UNIX shell commands are just wrapper programs for C function calls Why use the wrapper when you can use the real thing Secondly the C function calls return data in pointers and structures which are very easy to manipulate whereas piping the output of shell programs into others can be a very messy and awkward way of working Here are some of the reasons why we also need a more traditional programming language like C 1 The shell languages do not allow us to create an acceptable user interfa
41. first character of a line e There must be a TAB character at the beginning of every rule or action If there are spaces instead of tabs or no tab at all make will signal an error This bizarre feature can cause a lot of confusion Let s look at an example Makefile Ht Ht eH HH HH EH EH EH EH EE EE EH EH EH EE EH EH EE EE EE EH EE HE HE EE EH EE HE ydg ggg dd Makefile for the cfengine C Mark Burgess 1993 23 August 1994 revised Mark Ht Ht HH HH HH EE L EE EEE EH EH FE EE EE EH EE HE HE EH EH EE HE EH EH EE HEH HEADERS cf defs h PARSER cf y cf l OBJ cfengine o ifconf o N variables o classes o toolkits o X parsehandler o edittools o y tab o lex yy o CC cc LEX lex file Cl Dokumente und Einstellungen The UNIX programming environment htm 117 von 198 20 11 2004 11 29 42 The UNIX programming environment YACC yacc INSTALLDIR usr local BINDIR S INSTALLDIR bin SRCDIR INSTALLDIR cfengine CFLAGS DSUNA O Rules start here Note that the 0 variable becomes the name of the executable file In this case it is taken from the OBJ variable and expands to cfengine cfengine S OBJ S CC o 8 OBJ 11 ly S LDFLAGS The variable expands to the filename which needs to be compiled next lex yy c cf l S LEX y tab c cf y YACC d If a header file changes normally we need to recompile everything There is no
42. have keep identical copies of the data When it starts the ypbind process sends a broadcast request a call to all hosts on the network segment for a server which can serve the local NIS domain and waits for a response When a server replies with its IP address ypbind caches the answer in yp var binding domainname version ifthe directory exists All client programs which want to get information from the server can determine which server to query from this information The user level program ypwhich shows the name of the server the NIS services are currently bound to Some other user level commands are ypmatch mark passwd lookup entry for mark in passwd file ypcat hosts list hosts database The C library calls which query the databases are amongst others getpwnam get password data by name getpwuid get password data by uid getgrnam get group data by name gethostent get entry in hosts database getnetgrent get entry in netgroups database getservbyname get servive by name getservbyport get service by port get protobyname get protocol by name For a complete list and how to use these see the UNIX manual file Cl Dokumente und Einstellungen The UNIX programming environment htm 152 von 198 20 11 2004 11 29 42 The UNIX programming environment The following example shows how to read the password file of the system The functions used here can be used regardless of whether the network information service NIS is
43. in use The data are returned in a structure which is defined in usr include pwd h OK KK k k KKK KK KK HH ck Ck kk KC kc kc kc k ck kok k k X X ck kc k ck kc k kc kc kck ck ckckckckck ck k ck kk 15 da Read the passwd file by name and sequentially 9 x OK KK k k k k kk k k k ee ee ee k X X X k k k HK HH X ck ck ck ck ck kc k ck ck ck ckck KK kk include lt unistd h gt include lt pwd h gt main int uid Note in sys 5 type is uid t not int struct passwd bw uid getuid pw getpwuid uid printf Your login name is s n pw gt pw_name printf Now here comes the whole file n n setpwent while getpwent printf s3 3 s n pw gt pw_name pw gt pw_gecos pw gt pw_dir endpwent DNS The Domain Name Service The second network database service is that which converts host and domain names into IP numbers and vice versa This is the domain name service usually implemented by the BIND Berkeley Internet Name Domain software The information here concerns version 4 9 of this software The DNS or name service is implemented by a daemon called named which runs on a well known host Each domain must have at least one registered primary name server and usually has a number of secondary or backup nameservers All hosts must know the IP address of the nameserver in order to contact it file Cl Dokumente und Einstellungen The UNIX programming environment htm
44. is to decode this line Before looking at how to decode the data we should make an important point about the protocol line If a web browser does not get this Content type line from the CGI script it returns with an error 500 Server Error The server encountered an internal error or misconfiguration and was unable to complete your request file Cl Dokumente und Einstellungen The UNIX programming environment htm 105 von 198 20 11 2004 11 29 42 The UNIX programming environment Please contact the server administrator and inform them of the time the error occurred and anything you might have done that may have caused the error Error HTTPd malformed header from script www cgi bin comment pl Before finishing your CGI script you will probably ecounter this error several times A common reason for getting the error is a syntax error in your script If your program contains an error the first thing a browser gets in return is not the Content type line but an error message The browser does not pass on this error message it just prints the uninformative message above If you can get the above script to work then you are ready to decode the data which are sent to the script The first thing is to use perl to split the long line into an array of lines by splitting on amp We can also convert all of the symbols back into spaces The script now looks like this local bin perl Reply with proper protoco
45. largely the same as those for the C shell so we shall skip fairly quickly through the details Historically the Bourne shell came before the C shell profile The profile file is the Bourne shell s answer to csnrc This file is read by interactive bin sh shells on starting up On Sun systems the file etc profile is also read On HPUX machines the file etc src sh is read Variables and export file Cl Dokumente und Einstellungen The UNIX programming environment htm 61 von 198 20 11 2004 11 29 42 The UNIX programming environment Local and global variables are both defined using the syntax VARIABLE Some string VAR 13 It is important that there be no space between the variable and the equals sign By default these variables are local To make them global so that child processes will inherit them we use the command export VARIABLE This adds the variable to the process environment It is the analogue of making environment variables with setenv in C shell The command set a changes the default so that all variables after the command are created global Arrays or lists are often simulated in shell by sandwiching the colon symbol between items PATH bin usr bin etc local bin LD LIBARAY PATH usr lib usr openwin lib local lib but there is no real facility for arrays in the Bourne shell Note that the UNIX cut command can be used to extract the elements of the list Loops can
46. lseek kmem nl C_NPROC n_value 0 1 read kmem amp nproc sizeof nproc Allocate memory for the tables proc table struct proc calloci nproc sizeof Struct proc pstatus struct pst status calloc nproc sizeof struct pst status lseek kmem nl C_PROC n_value 0 IR 2 read kmem amp pt addr sizeof pt addr ee shot lseek kmem pt addr 0 if read kmem proc table sizeof struct proc nproc 0 perror read proc_table close kmem exit 1 printf USER PID CPU RSS STAT TIME COMMMAND n for offset 0 offset lt nproc offset 4 p struct proc amp proc table offset if pstat PSTAT PROC amp pstatus offset sizeof struct pst status 0 p gt p pid 1 Jb E continue else if p gt p_pid 0 amp amp already_seen_swapper 6 continue file C Dokumente und Einstellungen The UNIX programming environment htm 138 von 198 20 11 2004 11 29 42 The UNIX programming environment else already seen swapper 1 FormatOut struct pst status amp pstatus offset close kmem kokokokok k X ck kk kk kk CKCKCkc kc kCKCk 2 2 2 ck ck ck ck kk 2 k kc kc k ok ck KCkckckck ck ck kc k 2 k CK Ck kc k ko kok ckckckck ck ck 2 2 2 2 2 2 207 FormatOut p extract info from pst structure see 6 Fu struct pst status p struct passwd pw static char status 5 NULL i
47. must log in directly and supply a password in order to gain access privileges On a network where files are often accessible in principle to anyone the username root gets mapped to the user nobody who has no rights at all The file hierarchy Unix has a hierachical filesystem which makes use of directories and sub directories to form a tree The root of the tree is called the root filesystem or Although the details of where every file is located differ for different versions of unix some basic features are the same The main sub directories of the root directory together with the most important file are shown in the figure Their contents are as follows kin Executable binary programs On most systems this is a separate directory to usr bin In SunOS this is a pointer link to usr bin Jete Miscellaneous programs and configuration files This directory has become very messy over the history of UNIX and has become a dumping ground for almost anything Recent versions of unix have begun to tidy up this directory by creating subdirectories etc mail etc services etc usr This contains the main meat of UNIX This is where application software lives together with all of the basic libraries used by the OS JUS ban More executables from the OS usr local This is where users custom software is normally added sbin A special area for statically linked system binaries They are placed here to distinguish
48. n else print Use CTBL Q to interrupt Wi Don t use quotes Now shift default array ARGV to get arguments 1 by 1 while Sfile shift if file eq file replace print Findmark will not operate on itself next Save existing mode of file for later Sdev Sino Smode stat file open INPUT file warn Couldn t open file n open OUTPUT Soutputfile warn Can t open tmp Snotify 1 while lt INPUT gt if Sfindstring sk notify file Cl Dokumente und Einstellungen The UNIX programming environment htm 94 von 198 20 11 2004 11 29 42 FAY The UNIX programming environment print Fixing Stiles yas notify 0 s Sfindstring Sreplacestring g print OUTPUT close OUTPUT If nothing went wrong if outfile not empty move temp file to original and reset the file mode saved above if z Soutputfile rename Soutputfile file chmod mode file else print Warning file empty n Similarly we can search for lines containing a string Here is the grep program written in perl local bin perl grep as a perl program Check arguments etc while lt gt print if SARGV 1 The operator search string returns true if the search string is a substring of the default variable _ To search an arbitrary string we write if teststring
49. names are generally as short as possible so they seem pretty cryptic Some familar ones which DOS borrowed from unix include cd mkdir file Cl Dokumente und Einstellungen The UNIX programming environment htm 13 von 198 20 11 2004 11 29 41 The UNIX programming environment which change to a new directory and make a new directory respectively To list the files in the current directory you use ls To rename a file you move it mv old name new name Text editing and word processing Text editing is one of the things which people spend most time doing on any computer It is important to distingiush text editing from word processing On a PC or Macintosh you are perhaps used to Word or WordPerfect for writing documents Unix has a Word like program called 1 yx but for the most part Unix users do not use word processors It is more common in the unix community to write all documents regardless of whether they are letters books or computer programs using a non formatting text editor Unix word processors like Framemaker do exist but they are very expensive A version of MS Word also exists for some unices Once you have written a document in a normal text editor you call up a text formatter to make it pretty You might think this strange but the truth of the matter is that this two stage process gives you the most power and flexibilty and that is what most unix folks like For writing programs or anything else you edi
50. not equal test x gt y True if x is greater than y test x lt y True if xis less than y test x ge y True if x gt y test x le y True if x 2 y Logical NOT operator Logical AND Logical OR Note that an alternate syntax for writing these commands if to use the square brackets instead of writing the word test x lt y test x lt y The conditional structures have the following syntax if unix command then command else commands Fi The else clause is of course optional As noted before the first unix command could be anything since every command has a return code The result is TRUE if it evaluates to zero and false otherwise in contrast to the conventions in most languages Multiple tests can be made using if unix command then commands elif unix command file Cl Dokumente und Einstellungen The UNIX programming environment htm 66 von 198 20 11 2004 11 29 42 The UNIX programming environment then commands elif unix command then commands else commands fi where elif means else if The equivalent of the C school s switch statement is a more Pascal like case structure case unix command or variable in wildcardl commands wildcard2 commands wildcard3 commands esac This structure uses the wildcards to match the output of the command or variable in the first line The first pattern which matches gets executed Input from the user in sh In shell you ca
51. of the directories listed in the environment variable LD LIBRARY PATH Alternatively we can add a directory to the search path by using the L option cc o myprog files o lm lcurses 1BLAH L usr local lib Include files Normally the compiler looks for include files only in the directory usr include We can add further paths to search using the 1 option cc o myprog file c I usr local include I usr local X11 include Previously unix libraries have been in a out code format but recent releases of unix have gone over to a more efficient and flexible format called ELF executable and linking format Shared and static libraries The libraries the linker links with are simply collections of C functions which someone has written The source code for such a library is just the source for a collection of functions there is no main program To make an archive static library we compile all of the functions we wish to include in the library using cc c functionl c function2 c and then join the files using the ar command file Cl Dokumente und Einstellungen The UNIX programming environment htm 114 von 198 20 11 2004 11 29 42 The UNIX programming environment ar rcv libMYLIB a functionl o ar rcv libMYLIB a function2 o To make a shared library under SunOS we take the object files o and run ld o libMYLIB so 1 1 assert pure text o Under HPUX we write ld b o LIBMYLIB 86 1 1 7 6 NOTE when
52. of these cases it is assumed that the variable is to be split on whitespace characters In the second case we decide on what characterthe split is to take place and on what string the function is to act For instance inew array split name passwd uid gid gcos home shell The result is a seven element array called new_array where new array 0 iS name etc In the final example the left hand side shows that we wish to capture elements of the array in a named set of scalar variables If the number of variables on the lefthand side is fewer than the number of strings which are generated on the right hand side they are discarded If the number on the left hand side is greater then the remainder variables are empty Associated arrays One of the very nice features of Perl is the ability to use one string as an index to another string in an array For example we can make a short encyclopaedia of zoo animals by constructing an associative array in which the keys or indices of the array are the names of animals and the contents of the array are the information about them Sanimals Penguin A suspicious animal good with cheese crackers Sanimals dog Plays stupid but could be a cover if Sindex eq fish Sanimals index Often comes in square boxes Very cold An entire associated array is written array while the elements are array key Perl provides a special associat
53. standard is of the form struct hostent char h name official name of host char h aliases alias list int h_addrtype host address type int h_length length of address char h addr list list of addresses from name server define h addr h addr list 0 address for backward compatiblity The structure contains a list of addresses and or aliases from the nameserver The interesting guantity 1s usually extracted by means of the macro h_addr whcih gives the first value in the address list though officially one should examine the whole list now This value is a pointer which can be converted into a text form by the following hideous type transformation include lt sys types h gt include lt sys socket h gt finclude lt netinet in h gt struct sockaddr_in sin cin sin addr s addr istruot in_addr hp gt h addr s addtr file Cl Dokumente und Einstellungen The UNIX programming environment htm 155 von 198 20 11 2004 11 29 42 The UNIX programming environment printf IP address s n inet_ntoa cin sin_addr See the client program in the first section of this chapter for an example of its use Sun s network filesystem is maintained by a number of daemon processes NFS works on top of Sun s RPC Remote Procedure Call package Some of these daemons are named rpc something Some systems like Ultrix drop the rpc prefix The following list of names is b
54. stat h usr include dirent h and usr include sys types h Here are the most important structures struct dirent file Cl Dokumente und Einstellungen The UNIX programming environment htm 125 von 198 20 11 2004 11 29 42 The UNIX programming environment off_t d off offset of next disk dir entry ur unsigned long d fileno file number of entry unsigned short d reclen length of this record unsigned short d namlen length of string in d name char d_name 255 1 name up to MAXNAMLEN 1 struct stat dev_t st_dev device number ino t st ino file inode mode t st mode permission short st nlanks Number of hardlinks to file uid t st uid user id cud E st guid group d dev t st rdev Off t st size size in bytes time t st atime int st sparel time t st mtime int st Spare2 time t st ctime int st Spare3 long st blksize long st blocks long st spare4 2 Istat and readlink The function stat treats symbolic links as though they were the files they point to In other words if we use stat to read a symbolic link we end up reading the file the link points to and not the link itself we never see symbolic links To avoid this problem there is a different version of the stat function called 1stat which is identical to stat except that it treats links as links and not as the fil
55. system unix records information about who creates files and also who is allowed to access them later Each user has a unique username or loginname together with a unique user id or uid The user id is a number whereas the login name is a text string otherwise the two express the same information A file belongs to user A if it is owned by user A User A then decides whether or not other users can read write or execute the file by setting the protection bits or the permission of the file using the command chmod In addition to user identities there are groups of users The idea of a group is that several named users might want to be able to read and work on a file without other users being able to access it Every user is a member of at least one group called the ogin group and each group has both a textual name and a number group id The uid and gid of each user is recorded in the file etc passwd See chapter 6 Membership of other groups is recorded in the file etc group or on some systems etc logingroup Protection bits The following output is from the command 1s lag executed on a SunOS type machine lrwxrwxrwx 1 root wheel f Jun 1 1993 bin gt usr bin pepe l root bin 103512 Jun 1 1993 boot Orwxr sr x 2 bin Staff 11264 May 11 17 00 dev drwxr sr x 10 bin staff 2560 Jul 8 02 06 ete rwxr sr x 8 root wheel 512 Jun 1 1993 export Orwx 2 root daemon 512 Sep 26 1993 home rwxr xr x 1 root
56. take their input from the file stdin the keyboard and write their output to the file stdout and their error messages to the file stderr normally both of these output files are defined to be the current terminal device dev tty Or dev console stdin stdout and stderr known collectively as stdio can be redefined or redirected so that information is taken from or sent to a different file The output direction can be changed with the symbol gt For example echo testing myfile produces a file called my ile which contains the string testing The single gt greater than sign always creates a new file whereas the double gt gt appends to the end of a file if it already exists So the first of the commands echo blah blah myfile echo Newfile myfile adds a second line to my ile after testing whereas the second command writes over myfile and ends up with just one line Newfile file Cl Dokumente und Einstellungen The UNIX programming environment htm 40 von 198 20 11 2004 11 29 42 The UNIX programming environment Now suppose we mistype a command ehco test myfile The command ehco does not exist and so the error message ehco Command not found appears on the terminal This error message was sent to stderr so even though we redirected output to a file the error message appeared on the screen to tell us that an error occurred Even this can be change
57. the file into a column of a table For instance paste one two three would make a table in which the first column consisted of all lines in one the second of all lines in two and the third of all lines in three If one file is longer than the others then some columns have blank spaces Perl unifies all of these operations and more It also makes them much simpler Program structure To summarize Perl we need to know about the structure of a Perl program the conditional constructs it has its loops and its variables In the latest versions of Perl Perl 5 you can write object oriented programs of great complexity We shall not go into this depth for the simple reason that Perl s strength is not as a general programming language but as a specialized language for textfile handling The syntax of Perl is in many ways like the C programming language but there are important differences e Variables do not have types They are interpreted in a context sensitive way The operators which acts upon variables determine whether a variable is to be considered a string or as an integer etc e Although there are no types Perl defines arrays of different kinds There are three different kinds of array labelled by the symbols and e Perl keeps a number of standard variables with special names e g _ ARGV and ENV Special attention should be paid to these They are very important e he shell reverse apostrophe notatio
58. the shell is to provide a user interface with access to the system s facilities at a simple level In the 70 s user interfaces were not deisgned to be user friendly The UNIX shell is not particularly use friendly but it is very powerful Perhaps it would have been enough to provide only commands to allow users to write C programs Since all of the system functions are available from C that would certainly allow everyone to do what anything that UNIX can do But shell programming is much more immediate than C It is an environment of frequently used tools Also for quick programming solutions C is a compiled language whereas the shell is an interpreter A quick shell program can solve many problems in no time at all without having to compile anything Shell programming is only useful for quick and easy programs To use it for anything serious is an abuse Programming difficult things in shell is clumsy and it is difficult to get returned information like error messages back in a useful form Besides shell scripts are slow compared to real programs since they involve starting a new program for each new command These difficulties are solved partly by Perl which we shall consider next but in the final analysis real programs of substance need to be written in C Contrary to popular belief this is not more difficult than programming in the shell in fact many things are much simpler because all of the shell commands originated as C fun
59. versions of UNIX You should check the manual page man sticky to find out about your system The following is common behaviour file Cl Dokumente und Einstellungen The UNIX programming environment htm 36 von 198 20 11 2004 11 29 42 The UNIX programming environment For executable files the setuid bit tells UNIX that regardless of who runs the program it should be executed with the permissions and rights of owner of the file This is often used to allow normal users limited access to root privileges A setuid root program is executed as root for any user The setgid bit sets the group execution rights of the program in a similar way In BSD unix if the setgid bit is set on a directory then any new files created in that directory assume the group ownership of the parent directory and not the logingroup of the user who created the file This is standard policy under system 5 A directory for which the sticky bit is set restrict the deletion of files within it A file or directory inside a directory with the t bit set can only be deleted or renamed by its owner or the superuser This is useful for directories like the mail spool area and tmp which must be writable to everyone but should not allow a user to delete another user s files Ultrix If an executable file is marked with a sticky bit it is held in the memory or system swap area It does not have to be fetched from disk each time it is executed This saves time for frequently used p
60. way that make can know this unless we write a rule which forces it to rebuild all o files if the header file changes A de de db ob OBJ S HEADERS As well as special rules for special files we can also define a suffix rule This is a rule which tells us how to build all files of a certain type Here is a rule to get o files from c files The variable is like but is only used in suffix rules dE db db db db o S CC c S CFLAGS lt EE E E E E E E E E E TE 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 272 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 222 2 2 2 2 20 Clean up install kk k k HH file Cl Dokumente und Einstellungen The UNIX programming environment htm 118 von 198 20 11 2004 11 29 42 The UNIX programming environment Make can also perform ordinary shell command jobs make tidy here performs a cleanup operation tidy d l OBJ y tab c lex yy c y tab h y tab lex yy 9 xz Kw o Es Il d l mconfig tab c mconfig tab h a out man dvi man aux man log man toc cfengine tar gz cfengine tar cfengine tar Z d l Fh FH Fh Fh Fh Fh Fh Rede tka SER d obs d d l clean make tidy rm f cfengine install if f BINDIR cfengine then X In s S SRCDIR cfengine BINDIR cfengine I3 tar make clean cd tar cf tmp gfengine tar cfenginue compress tmp cfengine tar cp tmp cfengine tar Z rm tmp cfengine tar Z docume
61. way to learn about these statements is to use them so we shall now look at some examples bin csh f file Cl Dokumente und Einstellungen The UNIX programming environment htm 52 von 198 20 11 2004 11 29 42 The UNIX programming environment Safe copy from lt arg 1 gt to lt arg 2 gt if S argv 2 then echo Syntax copy lt from file gt lt to file gt exit 0 endif if f Sargv 2 then echo File exists Copy anyway switch lt Get a line from user case y breaksw default echo Doing nothing exit 0 endsw endif echo n Copying argv 1 to argv 2 cp argv 1 argv 2 echo done endif This script tries to copy a file from one location to another If the user does not type exactly two arguments the script quits with a message about the correct syntax Otherwise it tests to see whether a plain file has the same name as the file the user wanted to copy to If such a file exists it asks the user if he she wants to continue before proceding to copy Switch example configure script Here is another example which compiles a software package This is a problem we shall return to later See section Make The problem this script tries to address is the following There are many different versions of UNIX and they are not exactly compatible with one another The program this file compiles has to work on any kind of UNIX so it tries first to determine what kind of UNIX system the script is
62. wheel 249079 Jun 1 1993 kadb lrwxrwxrwx 1 root wheel 7 Jun 1 1993 lib gt usr lib drwxr xr x 2 root wheel 8192 Jun 1 1993 lost found drwxr sr x 2 bin staff 512 Jul 23 1992 mnt dr xr xr x 1 root wheel 512 May 11 17 00 net rwxr sr x 2 root wheel 512 Jun 1 1993 DOES drwxr sr x 2 bin staff 512 Jun 1 1993 sbin lrwxrwxrwx 1 root wheel 13 Jun 1 1993 sys gt kvm sys drwxrwxrwx 6 root wheel 732 Jul 8 19 23 tmp file Cl Dokumente und Einstellungen The UNIX programming environment htm 33 von 198 20 11 2004 11 29 42 The UNIX programming environment drwxr xr x 27 root wheel 1024 Jun 14 1993 usr drwxr sr x 10 bin staff 512 Jul 23 1992 var rwxr xr x 1 root daemon 2182656 Jun 4 1993 vmunix The first column is a textual representation of the protection bits for each file Column two is the number of hard links to the file See exercises below The third and fourth columns are the user name and group name and the remainder show the file size in bytes and the creation date Notice that the directories bin and sys are symbolic links to other directories There are sixteen protection bits for a UNIX file but only twelve of them can be changed by users These twelve are split into four groups of three Each three bit number corresponds to one octal number The leading four invisible bits gives information about the type of file is the file a plain file a directory or a link In the output from 1s this is represented by a single character
63. your string When opening files it is common to see the syntax open filehandle Filename die Can t open The logical oR symbol is used because open returns true if all goes well in which case the right hand side is never evaluated If open is false then die is executed You can decide for yourself whether or not you think this is good programming style we mention it here because it is common practice The stat idiom The unix library function scat is used to find out information about a given file This function is available both in C and in Perl In perl it returns an array of values Usually we are interested in knowing the access permissions of a file scat is called using the syntax array stat filename or alternatively using a named array Sdevice Sinode Smode stat filename The value returned in the mode variable is a bit pattern See section Protection bits The most useful way of treating these bit patterns is to use octal numbers to interpret their meaning To find out whether a file is readable or writable to a group of users we use a programming idiom which is very common for dealing with bit patterns first we define a mask which zeroes out all of the bits in the mode string except those which we are specifically interested in This is done by defining a mask value in which the bits we want are set to 1 and all others are set to zero Then we AND the mask with the mode stri
64. 04 11 29 41 The UNIX programming environment shell Shells A shell is a command interpreter In the early days of unix a shell was the only way of issuing commands to the system Nowadays many window based application programs provide menus and buttons to perform simple commands but the UNIX shell remains the most powerful and flexible way of interacting with the system After logging in and entering a password the unix process init starts a shell for the user logging in Unix has several different kinds of shell to choose from so that each user can pick his her favourite command interface The type of shell which the system starts at login is determined by the user s entry in the passwd database On most systems the standard login shell is a variant of the C shell Shells provide facilities and commands which Start and stop processes programs Allow two processes to communicate through a pipe Allow the user to redirect the flow of input or output Allow simple command line editing and command history Define aliases to frequently used commands Define global environment variables which are used to configure the default behaviour of a variety of programs These lie in an associated array for each process and may be seen with the env command Environment variables are inherited by all processes which are started from a shell e Provide wildcard expansion joker notation of filenames using e Provide a simple
65. 18 signal from the keyboard 5 You can suspend any number of programs file Cl Dokumente und Einstellungen The UNIX programming environment htm 48 von 198 20 11 2004 11 29 42 The UNIX programming environment and then restart them one at a time using g and bg If you want job 5 to be restarted in the foreground you would type fg 5 When you have had enough of job 5 you can type CTRL z to suspend it and then type fg 6 to activate job 6 Provided a job does not want to send output to stdout you can restart any job in the background using a command like bg 4 This method of working was useful before windows were available Using g and bg you can edit several files or work on several programs without have to quit to move from one to another See also some related commands for batch processing at batch and atq cron NOTE CTRL c sends a kill 2 signal which send a standard interrupt message to a program This is always a safe way to interrupt a shell command Scripts with arguments One of the useful features of the shell is that you can use the normal unix commands to make programs called scripts To make a script you just create a file containing shell commands you want to execute and make sure that the first line of the file looks like the following example bin csh f A simple script check for user s mail set path bin usr ucb Set the local path cd va
66. E Sguestbook_page iu nexus ud mark www tmp cfguest html Stmp_page iu nexus ud mark www tmp guests tmp Sremote_host SENV REMOTE_HOST file Cl Dokumente und Einstellungen The UNIX programming environment htm 108 von 198 20 11 2004 11 29 42 The UNIX programming environment print Content type text html n n print lt br gt lt hr gt lt br gt n print Thank you for submitting your comment lt br gt lt br gt n print best wishes lt br gt lt br gt print Mark lt br gt lt br gt lt br gt print Return to lt a href http www iu hioslo no mark menu html gt menu lt a gt n Sargs lt STDIN gt input s g Sinput s g Garray split amp Sinput skip name split varl Sarray 0 skip message split var2 S Sarray 1 if open PAGE guestbook page print Content type text html n n print couldn t open guestbook page file if open TMP gt tmp_page print Content type text html n n print couldn t open temporary output file while Sline lt PAGE gt if Sline h3 Number of entries J7 Sentry_no 1 Sentry no Sline lt h3 gt Number of entries S entry no lt h3 gt n if line LAST ENTRY gt Sdate date A b d Y print TMP lt b gt Entry date from host Sremote_host lt b gt n lt p gt n print TMP From name n
67. EH EE SIE EEE OEE HEE HE EOE EEE 2 E GE Level 2 Hatt HH HHH EHH EH EH EH OE EH OE EH OE RE EE EE HEE HE EE EE EEE ERE ERE ER E GE ReallyQuit while true do echo Do you really want to quit read answer case Sanswer in file Cl Dokumente und Einstellungen The UNIX programming environment htm 71 von 198 20 11 2004 11 29 42 The UNIX programming environment yr X return OF echo Resuming return 1 esac done Het HH HHH HE HH EE HE HE EE EH EH EE EH OE EE EEE ZZ Level 1 Hatt HH HHH HE HH EH EH EE EH EE CH OE EH OE EE HEE HOH OE L EE EE EH OEE SignalHandler if ReallyQuit Call a function then exit 0 else return 0 fi HEH HE HE HH HH HEHE HE HE HH HH EH HH HH EE EE HE EH HH HH EEE EH EE HH HE Level 0 main program HEH HE HH HH HH tH EE HE HH HH HH HH HH EE EE EH HH HOH EEE HE EH EHEH trap SignalHandler 2 15 Trap kill signals 2 and 15 echo Type some lines of text while read text do echo Stext CTRL C to exit done Note that the logical tree structure of this program is upside down the highest level comes at the bottom This is because all subroutines must be defined before they are used This example concludes our brief survey of the Bourne shell setuid and setgid scripts file Cl Dokumente und Einstellungen The UNIX programming environment htm 72 von 198 20 11 2004 11 29 42 The UNIX programming environment The superuser root is the only
68. Forking new processes e Formatting text in a file e Forms in HTML e ftp program e FTP resources finding e Fully qualified name e g e gcc e gdb debugger e getenv function e getgrnam e gethostbyname gethostbyname e gethostent e getnetgrent e getpwnam e getpwuid file Cl Dokumente und Einstellungen The UNIX programming environment htm 187 von 198 20 11 2004 11 29 42 The UNIX programming environment e getservbyname e getservbyport e Getting command output into a string e ghostscript GNU postscript interpreter e ghostview postscript previewer e gif e Global variables e Global variables in csh e Global variables in sh e Granting permission e groups e halt command e Hard links Hard links e Help function for commands e Hierarchy file e hostname command e Hypertext e O streams e if in perl e if then elseincsh e if then else fiinsh e ifconfig command e IFS variable in sh e INADDR ANY e Include file search path e Include files e Index nodes e Information about file properties e init e inittab e inodes e Input in csh e Input in sh e Input over many lines e Inserting a command into a string e Internet relay chat e Internet resources file Cl Dokumente und Einstellungen The UNIX programming environment htm 188 von 198 20 11 2004 11 29 42
69. NIX programming environment htm 124 von 198 20 11 2004 11 29 42 The UNIX programming environment main if yyin fopen My_Input_File r NULL Open file printf Can t open file n exit 1 while feof yyin yyparse fclose yyin Files and directories opendir readdir Files and directories are handled by functions defined in the header file dirent n In earlier UNIX systems the file dir n was used and the definitions were slightly different To get a list of files in a directory we must open the directory and read from it just like a file A directory is just a file which contains data on its entries The commands are opendir closedir readdir See the manual pages for dirent These functions return pointers to a dirent structure which is defined in the file usr include dirent h To determine the file statistics we use the function call stat or its corollory Istat Both these functions find out information about files permissions owner filetype etc The only difference between them is the way in which they treat symbolic links If scat is used on a symbolic link it stats the file the link points to rather than the link itself If 1st at is used the data refer to the link Thus to detect a link we must use 1stat See section Istat and readlink System structs The data in the sta structure are defined in the files usr include sys
70. TRL C file Cl Dokumente und Einstellungen The UNIX programming environment htm 21 von 198 20 11 2004 11 29 42 The UNIX programming environment Interrupt or break key Sends signal 15 to a process CTRL D Signifies EOF end of file or shows expansion matches in command filename completion See section Command filename completion CTRL E Jump to end of line CTRL L Clear screen in newer shells and in emacs Same as clear in the shell CTRL Z Suspend the present process but do not destroy it This sends signal 18 to the process Alternative shells bash The Bourne Again shell an improved sh csh The standard C shell jsh The same as sh with C shell style job control ksh The Korn shell an improved sh sh The original Bourne shell sh5 On ULTRIX systems the standard Bourne shell is quite stupid sh5 corresponds to the normal Bourne shell on these systems tcsh An improved C shell zsh An improved sh Window based terminal emulators xterm The standard X11 terminal window shelltool cmdtool Openwindows terminals from Sun Microsystems These are not completely X11 compatible during copy paste operations screen This is not a window in itself but allows you to emulate having several windows inside a single say xterm window The user can switch between different windows and open new ones but can only see one window at a time See section Multiple screens Remote shells and logins rlogin Login onto a rem
71. The UNIX programming environment The UNIX programming environment Edition 2 0 June 1997 Mark Burgess Centre of Science and Technology Faculty of Engineering Oslo College Copyright C 1996 7 Mark Burgess Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying provided also that the section entitled GNU General Public License is included exactly as in the original and provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one Permission is granted to copy and distribute translations of this manual into another language under the above conditions for modified versions except that the section entitled GNU General Public License may be included in a translation approved by the author instead of in the original English Foreword This is a revised version of the UNIX compendium which is available in printed form and online via the WWW and info hypertext readers It forms the basis for a one or two semester course in UNIX The most up to date version of this manual can be found at http www iu hioslo no mark unix html It is a reference guide which contains enough to help you to find what you need from other sources It is not and probably can neve
72. The UNIX programming environment htm 18 von 198 20 11 2004 11 29 42 The UNIX programming environment It is important to understand that the shell expands wildcards When you type a command the program is not invoked with an argument that contains or The shell expands the special characters first and invokes commands with the entire list of files which match the patterns The programs never see the wildcard characters only the list of files they stand for To see this in action you can type echo etc rc which gives etc rc etc rc boot etc rc ip etc rc local etc rc local etc rc local etc rc single etc rc All shell commands are invoked with a command line of this form This has an important corollary It means that multiple renaming cannot work Unix files are renamed using the mv command In many microcomputer operating systems one can write rename x y which changes the file extension of all files ending in x to the same name with a y extension This cannot work in unix because the shell tries expands everything before passing the arguments to the command line The local shell variable nog1ob switches off wildcard expansion in the C shell but you still cannot rename multiple files using mv Some free software programs make this possible Regular expressions The wildcards belong to the shell They are used for matching filenames UNIX has a more general and widely used mechanism for matching strings t
73. This is the button you normally use middle finger Used to pull down menus It is also used to paste a marked area somewhere at the mouse position outer finger Pulls down menus On a left handed system right and left are reversed E mail Reading electronic mail on unix is just like any other system but there are many programs to choose from There are very old programs from the seventies such as mail and there are fully graphical mail programs such as tkrat mailtool Choose the program you like best Not all of the programs support modern multimedia extensions because of their age Some programs like tkrat have immediate mail notification alerts To start a mail program you just type its name If you have an icon bar you can click on the mail icon Simple commands Inexperienced computer users often prefer to use file manager programs to avoid typing anything With a mouse you can click your way through directories and files without having to type anything e g the mgr or tkdesk programs More experienced users generally find this to be slow and tedious after a while and prefer to use written commands Unix has many short cuts and keyboard features which make typed commands extremely fast and much more powerful than use of the mouse If you come from a DOS environment the unix commands can be a little strange Because they stem from an era when keyboards had to be hit with hammer force and machines were very slow the command
74. X programming environment htm 7 von 198 20 11 2004 11 29 41 The UNIX programming environment Most of the unix kernel and daemons are written in the C programming language 1 Calls to the kernel and to services are made through functions in the standard C library The commands like chmod mkdir and cd are all C functions The binary files of the same name bin chmod bin mkdir etc are just trivial wrapper programs for these C functions Until Solaris 2 the C compiler was a standard part of the UNIX operating system thus C is the most natural language to program in in a UNIX environment Some tools are provided for C programmers dbx A symbolic debugger Also gdb xxgdb ddd make A development tool for compiling large programs lex A lexer A program which generates C code to recognize words of text yacc A parser This is a tool which generates C code for checking the syntax of groups of textual words rpcgen A protocol compiler which generates C code from a higher level langauge for programming RPC applications Stdin stdout stderr Unix has three logical streams or files which are always open and are available to any program stdin The standard input file descriptor O stdout The standard output file descriptor 1 stderr The standard error file descriptor 2 The names are a part of the C language and are defined as pointers of type FILE include lt stdio h gt FILE stdin stdout stderr
75. aE PEPE HE FE E E E E E E E E E E E E E sub BeginWebPage print lt HTML gt n print lt BODY gt n file Cl Dokumente und Einstellungen The UNIX programming environment htm 97 von 198 20 11 2004 11 29 42 The UNIX programming environment Ht it HE HE Ht He ae FE FE eae FE aE E HE E HE HE FE FE FE EEE SHE aE EEE EE EEE sub EndWebPage print lt BODY gt n print lt HTML gt n LE FE E HE EEE AEE PE EEE EEE sub ReadNewMail while lt gt if Subject Search for subject line Extract subject text chop Slert sricht split _ print lt H1 gt right lt H1 gt n next elsif Search for anything anything next skip other headers print Generate WWW pages automagically The following program scans through the password database and build a standardized html page for each user it finds there It fills in the name of the user in each case Note the use of the lt lt operator for extended input already used in the context of the shell See section Pipes and redirection in csh This allows us to format a whole passage of text inserting variables at strategic places and avoid having to the print over many lines local bin perl Build a default home page for each user in etc passwd file Cl Dokumente und Einstellungen The UNIX programming environment htm 98 von 198 20 11 2004 11 29 42 The UNIX programming
76. ack such a password Choose instead something which is easy to remember Feel free to use the PIN number from your bankers card in your password This will leave you with fewer things to remember e g Ma9876rk Passwords can be up to eight characters long Some sites allow you to change your password anywhere Other sites require you to log onto a special machine to change your password dax dax passwd Change your password on host nexus You cannot change it here dax rlogin nexus password nexus passwd Changing password for mark Enter login password ww Enter new password x Reenter new passwd x You will be prompted for your old password and your new password twice If your network is large it might take the system up to an hour or two to register the change in your password so don t forget the old one right away Mouse buttons Unix has three mouse buttons On some PC s running Linux or some other PC unix there are only two but the middle mouse button can be simulated by pressing both mouse buttons file Cl Dokumente und Einstellungen The UNIX programming environment htm 12 von 198 20 11 2004 11 29 41 The UNIX programming environment simultaneously The mouse buttons have the following general functions They may also have additional functions in special software index finger This is used to select and click on objects It is also used to mark out areas and copy by dragging
77. ain information which relates to the local domain They do not contain information from outside the domain The databases comprise passwd The network wide password database which supplements etc passwd on each host group The network wide group database which supplements etc group netgroups file Cl Dokumente und Einstellungen The UNIX programming environment htm 151 von 198 20 11 2004 11 29 42 The UNIX programming environment These are groups of hosts and or users which are used only the the purpose of system administration They can be used as shorthands for large numbers of users in the password file or exports file etc See next chapter mail aliases Network wide mail data nicknames hosts This is used to supplement the etc hosts file which maps hostnames into IP addresses This file is essentially redundant when DNS is running and more and more systems use DNS exclusively ethers Used to map hostnames into ethernet addresses This is only used by diskless workstations and certain x terminals services This replaces the network service list in etc services protocols Replaces etc protocols networks Replaces etc networks automount Configuration files for the NFS automounter NIS has two main components a client end process called ypbind and the server end daemon ypserv In addition standard C library calls can be used to interrogate the NIS databases The server process is run by one or more machines which
78. and like chmod u x filename This command would set execute permissions for the owner of the file chmod ug x filename would set execute permissions for the owner and for any users in the same group as the file Note that script programs must also be readable in order to be executable since the shell has the interpret them by reading chown and chgrp These two commands change the ownership and the group ownership of a file Only the superuser can change the ownership of a file on most systems This is to prevent users from being able to defeat quota mechanisms On some systems which do not implement quotas ordinary users can give a file away to another user but not get it back again The same applies to group ownership Making a group Normally users other than root cannot define their own groups This is a weakness in Unix from older times which no one seems to be in a hurry to change At Oslo College Computer Science we use a local solution whereby users can edit a file to create their own groups This file is called iu nexus local iu etc iu group The format of the group file is group name group number comma separated list of users s bit and t bit sticky bit The s and t bits have special uses They are described as follows Octal Text Name 4000 chmod u s Setuid bit 2000 chmod g s Setgid bit 1000 chmod t Sticky bait The effect of these bits differs for plain files and directories and differ between different
79. ased on Sun s own naming scheme portmap The RPC portmapper Converts RPC program numbers into ports keyserv Public key server rpc mountd Handles access control and file handles who is allowed to access the filesystem The mount daemon also performs pathname translation so that when we moun a network filesystem on a directory on our local host the resulting filenames of the mounted system translate correctly back into the pathnames of the original system automount Mounts filesystems automatically only when they are needed rpc nfsd This is the workhorse which actually sends data across the network nfsd services nfs requests for any client altering the filesystem physically rpc pcnfsd A server which implements basic nfs services for DOS environments This includes password authentification and printer services rpc bootparamd Obtains boot configuration data for diskless Sun workstations This is distinct from the bootp and tftp protocols used by other manufacturers rpc rquotad Informs on quotas for remote filesystems To establish a connection with a remote filesystem NFS uses the standard UNIX method of mounting filesystems A client wishing to mount a remote filesystem sends a mount request to the server s mount daemon This daemon verifies that the caller has permission to mount the filesystem and translates the pathnames of the files appropriately The mount daemon then returns an NFS file handle which subsequent read wr
80. ator for integers and the corresponding operator for strings eq These do not work in each other s places so if you get the wrong comparison operator your program might not work and it is quite difficult to find the error chop The command chop cuts off the last character of a string This is useful for removing newline characters when reading files etc The syntax is chop chop 5 chop scalar 4 remove last character in scalar Perl subroutines Subroutines are indicated as in the example above by the ampersand amp symbol When parameters are passed to a Perl subroutine they are handed over as an array called _ Which is analogous to the variable Here is a simple example local bin perl Sa silver Sb gold amp PrintArgs a b end of main sub PrintArgs local a 10cal b _ print 3160313 Slooal bin die exit on error When a program has to quit and give a message the die command is normally used If called without an argument Perl generates its own message including a line number at which the error occurred To include your own message you write die My message If the string is terminated with a Nn newline character the line number of the error is not file Cl Dokumente und Einstellungen The UNIX programming environment htm 87 von 198 20 11 2004 11 29 42 The UNIX programming environment printed otherwise Perl appends the line number to
81. ave mastered the unix interface and philosophy you will find that i the PC and Macintosh window environments seem to be easy to use but simplistic and primitive by comparison ii UNIX is far from being the perfect operating system it has a whole different set of problems and flaws The operating system of the future will not be UNIX as we see it today nor will is be DOS or Macintosh but one thing is for certain it will owe a lot to the UNIX operating system and will contain many of the tools and mechanisms we shall describe below Flavours of unix Unix is not a single operating system It has branched out in many different directions since it was introduced by AT amp T The most important fork in its history happened early on when the university of Berkeley California created the BSD Berkeley Software Distribution adding network support and the C shell Here are some of the most common implementations of unix BSD Berkeley BSD SunOS Sun Microsystems BSD sys 5 Solaris Sun Microsystems Sys 5 BSD Ultrix Digital Equipment Corperation BSD OSF 1 Digital Equipment Corperation BSD sys 5 HPUX Hewlett Packard Sys 5 AIX IBM Sys 5 BSD IRIX Silicon Graphics Sys 5 Linux GNU BSD Posix How to use this reference guide This programming guide is something between a user manual and a tutorial The information contained here should be sufficient to get you started with the unix system but it is far from
82. be read with the C call readlink See section Istat and readlink If we remove the file a symbolic link points to the link remains it just points nowhere Hard links A hard link is a duplicate inode in the filesystem which is in every way equivalent to the original file inode If a file is pointed to by a hard link it cannot be removed until the link is removed If a file has Qmath n hard links all of them must be removed before the file can be removed The number of hard links to a file is stored in the filesystem index node for the file Getting started If you have never met unix or another multiuser system before then you might find the idea daunting There are several things you should know Logging in Each time you use unix you must log on to the system by typing a username and a password Your login name is sometimes called an account because some unix systems implement strict quotas for computer resources which have to be paid for with real money 2 login mark password Once you have typed in your password you are logged on What happens then depends on what kind of system you are logged onto and how If you have a colour monitor and keyboard in front of you with a graphical user interface you will see a number of windows appear perhaps a menu bar You then use a mouse and keyboard just like any other system This is not the only way to log onto unix You can also log in remotely from another machine
83. bin perl Paste in perl Two files only syntax paste file 1file2 open filel ARGV 0 open file2 ARGV 1 die Can t open ARGV 0 n die Can t open ARGV 1 n while linel lt filel gt line2 lt file2 gt chop linel chop 11ine2 print Slinel Sline2 n tab character between Here we see more formally how to read from two separate files at the same time Notice that by putting the read commands into the test expression for the while loop we are using the fact that returns a non zero true value unless we have reached the end of the file To write and append to files we use the shell redirection symbols inside the open command open fd filename open file for writing open fd filename open file for appending We can also open a pipe from an arbitrary UNIX command and receive the output of that command as our input open fd bin ps aux A simple perl program file Cl Dokumente und Einstellungen The UNIX programming environment htm 85 von 198 20 11 2004 11 29 42 The UNIX programming environment Let us now write the simplest perl program which illustrates the way in which perl can save time We shall write it in three different ways to show what the short cuts mean Let us implement the cat command which copies files to the standard output The simplest way to write this is perl is the following local bin
84. ce like X windows or the curses cursor manipulation library They are mainly intended for file processing Though recently the Tk library has provided a way of creating user interfaces in Tcl and Perl 2 Shell commands read their input line by line Not all input is generated in this simple way we also need to be able to read through lines i e the concept of a data stream 3 More advanced data structures are needed for most applications such as linked lists and binary trees acyclic graphs etc 4 Compilers help to sort out simple typographical and logical errors by compile time checking source code 5 Compiled code is faster than interpreted code 6 Many tools have been written to help in the programming of C code dbx lex yacc etc C program structure The form of a C program AC program consists of a set of function beginning with the main program main This is a comment file Cl Dokumente und Einstellungen The UNIX programming environment htm 111 von 198 20 11 2004 11 29 42 The UNIX programming environment Commands C is a free format language which means you can write it in any way you like THIS IS NOT A GOOD IDEA If you are going to be effective in writing clear programs it is necessary to keep a discipline as we shall see in the next paragraph The source code of a C program can be divided into several text files C compiles all functions separately the linker joins them all up at the end
85. ces burdens on the resources of a computer since it expects to be able to run potentially many programs simultaneously If you are coming to UNIX from DOS you may well be used to using applications software or helpful interactive utilities to solve every problem UNIX is not usually like this the operating system has much greater functionality and provides the possibilities for making your own so it is less common to find applications software which implements the same things UNIX has long been in the hands of academics who are used to making their own applications or writing their own programs whereas as the DOS world has been driven by businesses who are willing to spend money on software For that reason commerical UNIX software is often very expensive and therefore not available at this college On the other hand the flexibility of UNIX means that it is easy to write programs and it is possible to fetch gigabytes of free software from the internet to suit your needs It may not look like what you are used to on your PC but then you have to file Cl Dokumente und Einstellungen The UNIX programming environment htm 2 von 198 20 11 2004 11 29 41 The UNIX programming environment remember that UNIX users are a different kind of animal altogether Like all operating systems UNIX has many faults The biggest problem for any operating system is that it evolves without being redesigned Operating systems evolve as more and more patches and hacks
86. ch does the job lex is a lexer It is normally used together with yacc 1ex tokenizes or identifies symbols in a file What that means is that it reads in a file and matches types of string in the file which are defined in terms of regular expressions by the programmer and returns symbolic values for those strings Although 1ex can be used by independently of yacc it is normally used to identify the different types of string which define the syntax of a file For example suppose yacc was parsing a C program On the beginning of a line it might expect to find either a variable name or a preprocessor symbol A variable name is just a string consisting of characters from the set 0 9a Z whereas a preprocessor command always starts with the character yacc passes control to 1ex which reads the file and matches the first object on the line If it finds a variable it returns to yacc a token which is a number or value corresponding to variable Similarly if it finds a preprocessor command it returns a token for that If it doesn t match either type it returns something else and yacc signals a syntax error Here is a yacc file which parses a file consisting of lines of the form a b where a and b are numbers any other syntax is incorrect We could have used this later in the example program for the client server example See section Sockets You can learn more about lex and yacc in Lex and Yacc
87. cket AF_INET SOCK_STREAM 0 1 perror socket exit 1 if bind sd amp sin sizeof sin 1 Must have this on server perror bind exit 1 Il Il l if listen sd queuesize perror listen file Cl Dokumente und Einstellungen The UNIX programming environment htm 149 von 198 20 11 2004 11 29 42 The UNIX programming environment SX L while true if sd client accept sd amp cin amp addrlen 1 perror accept exit 1 if recv sd_client buffer sizeof buffer D 1 perror recv exit 1 if DoService buffer break if send sd_client buffer strlen buffer 0 1 perror send exit 1 close sd client close sd printf Server closing down n KK KK KK k kk k k Ke HH KH HH HH ck ck ck kc kc kckckckckckckckck ck k kk DoService buffer char buffer This is the protocol section Here we must check that the incoming data are sensible int a 0 b 0 printf Received s n buffer sscant buffer sd Sd n 8a cb file Cl Dokumente und Einstellungen The UNIX programming environment htm 150 von 198 20 11 2004 11 29 42 The UNIX programming environment if a gt 0 amp amp b 0 sprintf buffer sd sa d a b atb return true else if strncmp halt buffer 4 0 sprintf buffer Server closing down retu
88. counterparts The syntax of these is if condition command if condition then command command else command command endif switch string case one commands breaksw case two commands breaksw file Cl Dokumente und Einstellungen The UNIX programming environment htm 51 von 198 20 11 2004 11 29 42 The UNIX programming environment endsw In the latter case no commands should appear on the same line as a case statement or they will be ignored Also if the bxeaksw commands are omitted then control flows through all the commands for case 2 case 3 etc exactly as it does in the C programming language We shall consider some examples of these statements in a moment but first it is worth listing some important tests which can be used in if questions to find out information about files ee pue True if the file exists and is readable w file True if the file exists and is writable tus file True if the file exists and is executable e file True if the file simply exists Ves file True if the file exists and is empty f file True if the file is a plain file d file True if the file is a directory We shall also have need of the following comparision operators is equal to string comparison is not equal to is greater than is less than isa is greater than or equal to VF is less than or equal to matches a wildcard does not match a wildcard The simplest
89. ctions The shell is an extra layer of the UNIX onion which we have to battle our way through to get where we re going file Cl Dokumente und Einstellungen The UNIX programming environment htm 73 von 198 20 11 2004 11 29 42 The UNIX programming environment Sometimes it is helpful to be shielded from ow level details sometimes it is a hindrance In the remaining chapters we shall consider more involved programming needs Exercises Write an improved which command in C shell Make a counter program which records in a file how many times you log in to your account You can call this in your cshrc file 3 Make a Bourne shell script to kill all the processes owned by a particular user Note that if you are not the superuser you cannot kill processes owned by other users 4 Write a script to replace the rm command with something safer Think about a way of implementing rm so that it is possible to get deleted files back again in case of emergencies This is not possible using the normal rm command Hint save files in a hidden directory deleted Make your script delete files in the Geleted directory if they are older than a week so that you don t fill up the disk with rubbish 5 Suppose you have a bunch of files with a particular file extension write a script in csh to change the extension to something else e g to change C into c Give the old and new extensions as arguments to the script 6 Write a p
90. d stderr can also be redirected by adding an ampersand amp character to the symbol The command ehco test gt amp myfile results in the file my ile being created containing the error message ehco Command not found The input direction can be changed using the lt symbol for example bin mail mark message would send the file message to the user mark by electronic mail The mail program takes its input from the file instead of waiting for keyboard input There are some refinements to the redirection symbols First of all let us introduce the C shell variable noclobber lfthis variable is set with a command like set noclobber then files will not be overwritten by the gt command If one tries to redirect output to an existing file the following happens unix set noclobber unix touch blah create an empty file blah unix echo test blah blah File exists If you are nervous about overwriting files then you can set noclobber in your cshrc file noclobber can be overridden using the pling symbol So unix set noclobber unix touch blah create an empty file blah unix echo test gt blah writes over the file b1an even though noclobber is set Here are some other combinations of redirection symbols eet file Cl Dokumente und Einstellungen The UNIX programming environment htm 41 von 198 20 11 2004 11 29 42 The UNIX programming environment Append inc
91. d hide the differences between different machines as far as possible But it has to be flexible enough to allow us to change all of the things we don t like to choose our own colours and the kind of window borders we want etc Other windowing systems like Microsoft windows ignore these problems and thereby lock the user to a single vendors products and a single operating system That of course is no accident The way X solves this problem is to use the client server model Each program which wants to open a window on somebody s compute screen is a client of the X window service To get something drawn on a user s screen the client asks a server on the host of interest to draw windows for it No client ever draws anything itself it asks the server to do it on its behalf There file Cl Dokumente und Einstellungen The UNIX programming environment htm 29 von 198 20 11 2004 11 29 42 The UNIX programming environment are several reasons for this e The clients can all talk a common window language or protocol We can hide the difference between different kinds of hardware by making the machine specific part of drawing graphics entirely a problem of implementing the server on the particular hardware When a new type of hardware comes along we just need to modify the server none of the clients need to be modified e We can contact different servers and send our output to different hardware thus even though a program is running
92. d later takes on the job of monitoring terminals for login requests starting new processes for these logins On some systems like HPUX a file etc inittab configures init and tells it to start other processes in addition to logins The configuration scripts are files called etc rc On BSD systems they are typically called rc rc boot and rc local On system 5 and POSIX based systems a new mechanism called inittab has been introduced and the concept of different run levels has been introduced In practice the effect is the same as the older rc files On a system with partitions these files lie on the root partition along with the kernel At this stage only the root partition is mounted These scripts bring the system up in one of two modes e Single user mode e Multi user mode In single user mode only the system administrator has access to the system no other logins are permitted The system mounts the root and usr partitions only and enters a shell This mode is used for debugging or for performing crucial operations for which the presence of other users would be a hindrance Single user mode is the ultimate critical section There is no virtual memory support in single user mode i e no swapping or paging When the single user shell is exited the system either reboots or switches to multi user mode by signalling init to permit other logins In multi user mode the configuration scripts Start th
93. dr sa family AF INET if sk socket AF_INET SOCK_DGRAM IPPROTO_IP 1 perror socket file Cl Dokumente und Einstellungen The UNIX programming environment htm 142 von 198 20 11 2004 11 29 42 The UNIX programming environment exit 1 if ioctl sk SIOCGIFFLAGS caddr t amp IFR 1 perror ioctl exit 1 We shall not go into the further details of ioctl but simply note its role in system programming Exercises Write a daemon program with a signal handler which makes a log of the heaviest maximum cpu process running every five minutes The program should exit if the log file becomes greater than 5 kbytes 2x Rewrite in C the perl program which lists all the files in the current directory containing a certain string 3 Write a version of more which prints control characters safely See the cat e command 4 file Cl Dokumente und Einstellungen The UNIX programming environment htm 143 von 198 20 11 2004 11 29 42 The UNIX programming environment Write a Makefile to create a shared library from a number of object files Network Programming The purpose of this chapter is to briefly describe the daemons which provide services for a TCP IP network and the essential mechanisms behind the Berkeley socket library Sockets The backbone of network communciation is the Berkeley socket mechanism Berkeley sockets are part of the standard C library Here we list t
94. ds ago The final command gives an absolute number The absolute command number can be seen by typing history file Cl Dokumente und Einstellungen The UNIX programming environment htm 43 von 198 20 11 2004 11 29 42 The UNIX programming environment Command filename completion In the tcsh extension of the C shell you can save hours worth of typing errors by using the completion mechanism This feature is based on the TAB key The idea is that if you type half a filename and press TAB the shell will try to guess the remainder of the filename It does this by looking at the files which match what you have already typed and trying to fill in the rest If there are several files which match the shell sounds the bell or beeps You can then type CTRL D to obtain a list of the possible alternatives Here is an example suppose you have just a single file in the current directory called very long filename typing more TAB results in the following appearing on the command line more very long filename The shell was able to identify a unique file Now suppose that you have two files called very long filename and very big filename typing more TAB results in the following appearing on the command line more very and the shell beeps indicating that the choice was not unique and a decision is required Next you type CTRL D to see which files you ahve to choose from and the shell lists them and returns you to the command line
95. e Snewext rm Sfile Soldext end file Cl Dokumente und Einstellungen The UNIX programming environment htm 59 von 198 20 11 2004 11 29 42 The UNIX programming environment rm r tmp chext Suser Here is another example to try to decipher Use the manual pages to find out about awk This script can be written much more easily in Perl or C as we shall see in the next chapters It is also trivially implemented as a script in the system administration language cfengine bin csh f HEH HEH HH HH tHE EH HH HE EH HH EE EE EEE EH HH HH EE HE EE HH HEE 1 2 2 KILL all processes owned by Sargv 1 with PID gt Sargv 2 HEH HE HH HH HH HEE EH HH HE HH HH OE EE EE E E EH HH HE EH EE HH HE OEE EE EE HH if whoami root then echo Permission denied exit 0 endif if S argv lt 1 S argv gt 2 then echo Usage KILL username lowest pid exit 0 endif if Sargv 1 root then echo No Too dangerous system will crash exit 0 endif HHH HEHE EHH HEE HH HE EE HH EE HH EE FE HE EE HH EE EH OE EE HH EEE HOHE EH HOE EH Kill everything HHH HHH EH HE HEE HHH EE EH HE EH HE EE HE EHH HEE EH EE EEE HEE EH HE EH HO EH if S argv then set killarray ps aux awk if 1 user printf Ss 2 user argv 1 gt foreach process killarray kill 1 process kill 15 process gt dev null kill 9 process gt dev null if kill 9 process egrep e No such process
96. e UNIX programming environment stat file amp statvar if S ISREG statvar mode plain file if S ISDIR statvar mode directory lstat file amp statvar if S ISLNK statvar mode symbolic link Command and Variable Index e _ insh e not e e insh e shell construction e in regular expressions e lt in make e in make e http nodevice com sections Programming unix html IDX803 e amp AND file Cl Dokumente und Einstellungen The UNIX programming environment htm 172 von 198 20 11 2004 11 29 42 The UNIX programming environment e incsh e in regular expressions e e in regular expressions e e e e e hel e e a insh e d file e sh e e file e eg insh e f file e f insh e g insh e ge insh e gt insh e h e le insh e 1lt insh e ne in sh e o insh e r file e r insh e s insh e u in sh e W file e w insh e x insh e z file file Cl Dokumente und Einstellungen The UNIX programming environment htm 173 von 198 20 11 2004 11 29 42 The UNIX programming environment e z in perl e inregular expressions e cshre e profile e xsession e bin e Ybinf ssh e bin sh e dev e devices e etc e etc group e etc passwd e export e home e sbin
97. e from ind and collect statistics over how many files there are in all of your sub directories Project Write a program which checks the sanity of your UNIX system 1 Check that the password file etc passwd is not writable by general users 2 Check that the processes cron and sendmail are running 3 Check that if the file etc exports or etc dfs dfstab exists the nfsd daemon is running 4 Check that if the filesystem table etc stab or its equivalent on non BSD systems contains NFS mounted filesystems the biod or nfsiod daemon is running 5 Check that the file etc resolv conf contains the correct domain name It may or may not be the same as that returned by the shell command domainname If it is not the same you should print the message NIS domain has different name to DNS domain WWW and CGI programming CGI stands for the Common Gateway Interface It is the name given to scripts which can be executed from within pages of the world wide web Although it is possible to use any language in CGI programs hence the word common the usual choice is Perl because of the ease with which Perl can handle text The CGI interface is pretty unintelligent in order to be as general as possible so we need to do a bit of work in order to make scripts work Permissions The key thing about the WWW which often causes a lot of confusion is that the W3 service runs with a user ID of nobody T
98. e g system 1s split Split a string variable into an array of elements by searching for a special character space or etc e g array split string rename Rename a file e g rename old name new name mkdir Make a new directory mkdir newdir shift Read the first element of an array and delete it shifting all the array elements down by one e g Sfirst shift array chop Chops off the last character of a string Often used for deleting the end of line character when reading from a file oct Interprets a number as octal converts to decimal e g decimal oct 755 kill Send a kill signal to a list of processes e g kill 9 pidi pid2 You should explore Perl s possibilities yourself Perl is a good alternative to the shell which has much of the power of C and is therefore ideal for simple and more complex system programming tasks If you intend to be a system administrator for UNIX systems you could do much worse than to read the Perl book and learn Perl inside out Summary The Practical Extraction and Report Language is a powerful tool which goes beyond shell programming but which retains much of the immediateness of shell programming in a more formal programming environment The success of Perl has led many programmers to use it exclusively In the next section would like to argue that programming directly in C is not much harder In fact it has advantages in the long run The power of Perl is t
99. e program in your action string gets started More generally you will want to create input boxes where you can type in data To create a single line input field you use the following syntax lt INPUT NAME variable name SIZE 40 gt This creates a single line text field of width 40 characters This is not the limit on the length of the string which can be typed into the field only a limit on the amount which is visible at any time It is for visual formatting only The NAME field is used to identify the data in the CGI script The string you enter here will be sent to the CGI script in the form variable name value of input Another type of input is a text area This is a larger box where one can type in text on several lines The syntax is lt TEXTAREA NAME variable name ROW 50 COLS 50 gt which means create a text area of fifty rows by fifty columns with a prompt to the left of the box Again the size has only to do with the visual formatting not to do with limits on the amount of text which can be entered As an example let s create a WWW page with a complete form which can be used to make a guest book or order form HTML HEAD lt TITLE gt Example form lt TITLE gt I Comment Mark Burgess 27 Jan 1997 LINK REV made HREF mailto mark iu hioslo no gt lt HEAD gt lt BODY gt lt CENTER gt lt H1 gt Write in my guest book lt H1 gt lt CENTER gt lt HR gt
100. e swapper Set the name of the system and the domainname of the network Configure the network interface Start the network services portmap inetd mountd etc Mount all remaining filesystems and disks Start accounting or quota checking if required file Cl Dokumente und Einstellungen The UNIX programming environment htm 158 von 198 20 11 2004 11 29 42 The UNIX programming environment e Load the X window system The shutdown procedure Anyone can start a UNIX machine but you must be the superuser in order to shut it down gracefully When shutting down the system it is polite to inform all users in advance so that they have a fighting chance to finish what they are doing and save their work Then all processes must be terminated then the disks must be synchronized with their caches then you can pull the plug The most important step from a hardware viewpoint is the disabling and synchronization of the disks If the power fails while the disk is writing data or before data have been written from the cache to the disk the filesystem could be damaged or even destroyed The commands for halting the system are halt Halt the system immediately and sync disks reboot Halt the system immediately sync disks and reboot sync Synchronize disk filesystems shutdown A polite form of halt which warns users to log out and kills processes carefully Under SunOS the shutdown command on NFS servers sends warning messages to all netw
101. e the command gcc o myprog a o b o c o So it looks for a o etc and doesn t find them It now goes to a kind of subroutine and looks to see if it has any rules for making files called o and it discovers that these are made by compiling with the gcc c option Since the files do not exist it does this Now the files a o b o c o exist and it jumps back to the original problem of trying to make myprog All the files it needs now exist and so it executes the command and builds myprog If we now edit a c and type make once again it goes through the same procedure as before file Cl Dokumente und Einstellungen The UNIX programming environment htm 116 von 198 20 11 2004 11 29 42 The UNIX programming environment but now it finds all of the files So it compares the dates on the files if the source is newer than the result it recompiles By using this recursive method make only compiles those parts of a program which need compiling Makefiles To write a Makefile we have to tell make about dependencies The dependencies of a file are all of those files which are required to build it Thus the dependencies of myprog are a o b o and c o The dependencies of a o are simply a c the dependencies of b o are b c and so on A Makefile consists of rules of the form filename or extension dependencies TAB rule There are two important things to remember e he file names must start on the
102. e unix kernel see below On HPUX systems with file is called hp ux On linux itis called 1inux kernel On newer systems the kernel is built up from a number of modules which are placed in this directory Every unix directory contains two virtual directories marked by a single dot and two dots ls The single dot represents the directory one is already in the current directory The double dots mean the directory one level up the tree from the current location Thus if one writes cd usr local Qd 2 the final directory is usr The single dot is very useful in C programming if one wishes to read the current directory Since this is always called there is no need to keep track of what the current directory really is and are hard links to the true directories Symbolic links A symbolic link is a pointer or an alias to another file The command file Cl Dokumente und Einstellungen The UNIX programming environment htm 10 von 198 20 11 2004 11 29 41 The UNIX programming environment ln s fromfile other directory tolink makes the file fromfile appear to exist at other directory tolink simultaneously The file is not copied it merely appears to be a part of the file tree in two places Symbolic links can be made to both files and directories A symbolic link is just a small file which contains the name of the real file one is interested in It cannot be opened like an ordinary file but may
103. earch in a global file database for files containing a search string whereis Look for a command and its documentation on the system Disk usage file Cl Dokumente und Einstellungen The UNIX programming environment htm 24 von 198 20 11 2004 11 29 42 The UNIX programming environment du Show number of blocks used by a file or files df Show the state of usage for one or more disk partitions Show other users logged on users Simple list of other users finger Show who is logged onto this and other systems who List of users logged into this system Long list of who is logged onto this system and what they are doing Contacting other users write Send a simple message to the named user end with CTRL D The command mesg n switches off messages receipt talk Interactive two way conversation with named user irc Internet relay chat A conferencing system for realtime multi user conversations for addicts and losers Mail senders readers mail The standard old mail interface Mail Another mail interface elm Electronic Mail program Lots of functionality but poor support for multimedia pine Pine Is No longer Elm Improved support for multimedia but very slow and rather stupid at times Some of the best features of elm have been removed mailtool Sun s openwindows client program rmail A mail interface built into the emacs editor netscape mail A mail interface built into the netscape navigator zmail
104. ector in perl e Arguments command line e argv e Arithemtic in sh e Arithemtic operations in csh e Arrays associated in perl e Arrays normal in perl e Arrays and split e Arrays in csh e Arrays in perl e Associated arrays iteration e at command e AT amp T e Automated mounts e awk e awk pattern extractor e Background picture e Background process Background process e Backwards quotes e bash bash e batch command e Berkeley Internet Name Domain BIND e bg command e BIND e bind e Booting a unix system e Bourne shell Bourne shell e Break key e breaksw e Browsing through a file e BSD file Cl Dokumente und Einstellungen The UNIX programming environment htm 183 von 198 20 11 2004 11 29 42 The UNIX programming environment e Build software script e Built in commands e C e C library calls and shell commands e C programming e C shell e C shell setup files e C suffix rules e C role in unix e Calculator shell e Calculator X windows e cat command e o NE e CGI protocol e Changing file mode e chgrp command e chgrp command e chmod command e chmod command e chop command in perl e chown command e chown command e close command in perl e closedir command e cmdtool e Command completion e Command history e Command interpreter e Command line arguments e Command line ar
105. egistered on Ht eH HEH k HE HE HE HE HE EE EH EE EEE EE EE EE EE EE EE E E EEE HE amp arguments die Xu if d home S5server Sdisks bin ls d home S server Sgroup foreach Shome split s disks open LS cd home bin ls home die allusers Pipe didn t file Cl Dokumente und Einstellungen The UNIX programming environment htm 91 von 198 20 11 2004 11 29 42 The UNIX programming environment n open while LS Sexists Suser split Sexists Spw Suid Sgid qu Scm gcos dir getpwnam Suser ww if Sexists if Sprinthomes print Sairat else print Suser n close LS FEFE E HE HE HE FE FE FE FE FE AE E FE E HE HE HE HE FE FE FE EAE AE E E TE TE EEE EEE TE E E E E E E E E E HE H E sub arguments Sprinthomes 0 group Es Sserver bin hostname chop server foreach Sarg ARGV if substr Sarg 0 1 eq u Sgroup Sarg next if Sarg eq home Sprinthomes 1 next Sserver Sarg default is to interpret as a server file Cl Dokumente und Einstellungen The UNIX programming environment htm 92 von 198 20 11 2004 11 29 42 The UNIX programming environment Searching and replacing text The sed like function for replacing all occurances of a string is easily implemented in Perl using while input s Ssearch Sreplace g print output
106. ehaviour We shall not go into great detail in this course only provide examples for reference The UNIX fork function is used to create child processes This is the basis of all heavyweight multitasking under unix Here is a simple example of fork in which we start a child process from within a program and wait for it to finish Note that the code for the parent and the child is is the same file The only thing that distinguishes parent from child is the value returned by the fork function When fork is called it duplicates the entire current process so that two parallel processes are then running The only difference between these is that the child process the copy gets a return value of zero from fork whereas the parent gets a return value equal to the process identifier pid of the child This value can be used by the parent to send messages or to wait for the child Here we show a simple example in which the wait NULL command is used to wait for the last child spawned by the parent KKK KK k k k kk KKK HH HH KH ee k X X X ck ck ck ck ck ck ck ck ckckckckckckck ck ck kk file Cl Dokumente und Einstellungen The UNIX programming environment htm 129 von 198 20 11 2004 11 29 42 The UNIX programming environment reos 27 A brief demo of the UNIX process duplicator fork A 2 x J KCKCKCKCK k k k k kk k KK HH CkCkCkCkCKCKCKCkCkCKCkCk HH ck ck ck k kc k ck ck ckckckckckckck ck kk include lt stdio
107. ellungen The UNIX programming environment htm 42 von 198 20 11 2004 11 29 42 The UNIX programming environment not mix synchronously Often stderr appears first tee and script Occasionally you might want to have a copy of what you see on your terminal sent to a file tee and script do this For instance find type 1 print tee myfile sends a copy of the output of find to the file myfile cee can split the output into as many files as you want command tee filel file2 You can also choose to record the output an entire shell session using the script command nexus script mysession Script started file is mysession nexus echo Big brother is scripting you Big brother is scripting you nexus exit exit Script done file is mysession The file mysession is a text file which contains a transcript of the session Command history The history feature in C shell means that you do not have to type commands over and over again In the tcsh version of the C shell and the basn version of the Bourne shell you can use the UP ARROW key to browse back through the list of commands you have typed previously In the normal C shell csn there are three main commands Execute the last command again leg Execute the third last command again 14 Execute command number 4 The first of these simply repeats the last command The second counts backwards from the last command to three comman
108. ely be a test but as before it could in principle be any UNIX command The until loop reminiscent of BCPL carries out a task until its argument evaluates to TRUE file Cl Dokumente und Einstellungen The UNIX programming environment htm 68 von 198 20 11 2004 11 29 42 The UNIX programming environment until unix command do commands done Finally the for structure has already been used above for variable in list do commands done Often we want to be able to use an array of values as the list which for parses but Bourne shell has no array variables This problem is usually solved by making a long string separated by for example colons For example the PATH variable has the form PATH usr bin bin local gnu bin Bourne shell allows us to split such a string on whatever character we wish Normally the split is made on spaces but the variable IFS can be defined with a replacement To make a loop over all directories in the command path we would therefore write IFS for name in PATH do commands done The best way to gain experience with these commands is through some examples bin sh Get text from user repeatedly echo Type away while read TEXT do echo You typed STEXT iqq MSIE RT Vea cp hen echo So I quit file Cl Dokumente und Einstellungen The UNIX programming environment htm 69 von 198 20 11 2004 11 29 42 The UNIX programming environment exit 0 fi
109. end sd buffer strlen buffer 0 1 perror send exit 1 if recv sd buffer bufsize 0 1 perror recv exit 1 printf Server responded with s n buffer close sd unlank socket KK KK k k k HH k k KH HH ck ck ck Ck k ck Ck Ck kc k ck kck HK ck ck k ck kk KK I ay The server part of a client server pair This simply takes two ur numbers and adds them together returning the result to the client n af file Cl Dokumente und Einstellungen The UNIX programming environment htm 148 von 198 20 11 2004 11 29 42 The UNIX programming environment Compiled with M CC Server c XJ OR KKK k HH k X X k k KH HK HH ck ck kk ck ck ck kc kc k ck kck KH ck kc k ck ck include lt stdio h gt include lt sys types h gt include lt sys socket h gt include lt netinet in h gt include lt netdb h gt define PORT 0x1234 define bufsize 20 define queuesize 5 define true 1 define false 0 KK KKK KKK HH HH KH KR eee ee HH KH HK HH ee KK ck kc KK KK KK f Main ey OK KKK k k KK KK k k HH k k HH eR HK HH HK KH KK ck KK main struct sockaddr_in cin struct sockaddr_in sin struct hostenr hp char buffer bufsize int sd sd client addrlen memset amp sin 0 sizeof sin Another way to zero memory Sin sin_family AF_INET sin sin addr s addr INADDR_ANY Broadcast address sin sin_port htons PORT if sd so
110. ents are very poor at performing this kind of service UNIX solves the problem of compiling enormous trees of software such as the unix system itself by using a compilation language called make Such language files can be generated automatically by scripts allowing very complex programs to configure and compile themselves from a single control script Compiling large projects Typing lines like cc c filel c file2 c file Cl Dokumente und Einstellungen The UNIX programming environment htm 115 von 198 20 11 2004 11 29 42 The UNIX programming environment ee target filelo repeatedly to compile a complicated program can be a real nuisance One possibility would therefore be to keep the command in a script This might we time wasting though Suppose you are working on a big project which consists of many lines of source code but are editing only one file You really only want to recompile the file you are working on and then relink all of the object files Recompiling files which haven t changed would be a waste of time But that means you have to change the script each time you change what you need to compile A better solution is to use the make command make was designed for precisely this purpose To use make we create a file called Makefile in the same directory as our program make is a quite general program for building software It is not specifically tied to the C programming language it can be used in any pro
111. environment Ht eH HH HH HH k I EEE EH HH EH EH EH HH EH FH EH HH EE EH FH HH tH FH 2 HF Level O main Ht HH HH HH HH HEH EH EH HH EH FH EH HH EE EH EH HH EH FH EH HH EH EH EH HH tH EH EH HH EE HF Strue 1 Sfalse 0 First build an associated array of users and full names setpwent while Strue Sname Spasswd Suid Sgid Squota comment fullname getpwent FullName name Sfullname print name FullName name n last if name eg print XI Now make a unique filename for each page and open a file foreach user sort keys FullName next if user eq print Making page for user n outputfile user html1 open OUT gt Soutputfile die Can t open Soutputfile n amp MakePage close OUT Hatt HH HHH HE HH EH EH EEE EEE RE HERE ERE RE HO EEE RE EE RE E ERE RE ERE RE ERE E E NER Level 1 Hatt HH HHH HEH H EH EH EE EE EE ERE EEE EE ERE ERE RE OH EE CH OEE HEE EH EE HOE EE RE EE RE RE ERE RE ERE RE E RE sub MakePage print OUT lt lt ENDMARKER file Cl Dokumente und Einstellungen The UNIX programming environment htm 99 von 198 20 11 2004 11 29 42 The UNIX programming environment HTML BODY HEAD gt lt TITLE gt SFullName Suser s Home Page lt TITLE gt lt HEAD gt H1 gt FullName user s Home Page lt Hl gt NA A A Hi welcome to my home page In case you hadn t got it yet my name is FullName use
112. environment breaksw case IRIX setenv TYPE IRIX setenv MAKE bin make breaksw default echo Unknown architecture SNAME 1 endsw Generate Makefile from source file sed s HOSTTYPE STYPE Makefile src Makefile echo Making software Type CTRL C to abort and edit Makefile SMAKE software call make to build program chmod 755 software set correct protection Loops in csh The C shell has three loop structures repeat while and foreach We have already seen some examples of the foreach loop The structure of these loops is as follows repeat number of times command while test expression commands end foreach control variable Iist or array commands end The commands break and continue can be used to break out of the loops at any time Here are some examples repeat 2 echo Yo write mark file Cl Dokumente und Einstellungen The UNIX programming environment htm 55 von 198 20 11 2004 11 29 42 The UNIX programming environment This sends the message Yo to mark s terminal twice repeat 5 echo echo Shutdown time Log out now wall sleep 30 halt This example repeats the command echo Shutdown time five times at 30 second intervals before shutting down the system Only the superuser can run this command Note the strange construction with echo echo This is to force the repeat command to take two shell commands as an argument Try to explain
113. es e Superuser e Suspending a job e Swapper e Swapping text strings e switch caseincsh e Symbolic links e System 5 e System administration e System details e System identity and uname e System name e System V e t bit e TAB completion key e talk service e ICL e TCP IP e tcsh tcsh e tee command e Teletype terminal e telnet e telnet e Terminal echo and stty e Terminals e test insh e test programs e test don t call your program this e Testing files e Testing reponse from other hosts e Tests and conditions in csh e Tests in sh e tex file Cl Dokumente und Einstellungen The UNIX programming environment htm 195 von 198 20 11 2004 11 29 42 The UNIX programming environment e texinfo system e Text form of access bits e Text formatting e textedit e The arguement vector in C e The domain name service e tiff e Time and date e Time stamp updating e Tk library e touch command e Traps in sh e Truncating strings in perl e ty e type in DOS e Types in perl e umask variable umask variable e uname command e Undefining variables e undelete e UNIX e UNIX history e unless in perl e unlink command e unset command e until e Up arrow e Updating file time stamp e User database support e User environment e users command e Variables global e Variables local e vi e Viewing a file e vmstat
114. es they point to This means that we can test whether a file is a symbolic link only if we use 1stat See the next paragraph Once we have identified a file to be a symbolic link we use the readlink function to obtain the name of the file the link points to define bufsize 512 char buffer bufsize readlink path to file buffer bufsize file Cl Dokumente und Einstellungen The UNIX programming environment htm 126 von 198 20 11 2004 11 29 42 The UNIX programming environment The result is returned in the string buffer stat test macros As we have already mentioned the UNIX mode bits contain not only information about what permissions a file has but also bits describing the type of file whether it is a directory or a link etc There are macros defined in UNIX to extract this information from the st mode member of the stat structure They are defined in the stat n headerfile Here are some examples define define define define define define define define define define define define define define define define define define define S_ISBLK S_ISCHR m S_ISDIR S ISP ILE S_ISREG S_ISLNK m O m 3 m S_ISSOCK m S IRWXU S IRWXG S IRWXO 9 IRUSR S IWUSR 9 IXUSR S_IRGRP S_IWGRP S_IXGRP S IROTH S IWOTH S IXOTH is is is is is is is
115. es two different ways of writing the i command in perl The default scalar variable The special variable _ is used for many purposes in Perl It is used as a buffer to contain the result of the last operation the last line read in from a file etc It is so general that many functions which act on scalar variables work by default on if no other argument is specified For example Print file Cl Dokumente und Einstellungen The UNIX programming environment htm 77 von 198 20 11 2004 11 29 42 The UNIX programming environment is the same as print Array vector variables The complement of scalar variables is arrays An array in Perl is identified by the symbol and like scalar variables is allocated and initialized dynamically array 0O This little piggy went to market array 2 This little piggy stayed at home print array 0 array 1 array 2 The index of an array is always understood to be a number not a string so if you use a non numerical string to refer to an array element you will always get the zeroth element since a non numerical string has an integer value of zero An important array which every program defines is ARGV This is the argument vector array and contains the commands line arguments by analogy with the C shell variable Sargv Given an array we can find the last element by using the operator For example S last element SARGV S ARGV
116. f configuring terminals is much easier now that hardware is more standard Users terminals are usually configured centrally by the system administrator and it is seldom indeed that one ever has to choose anything other than vc 100 or xterm file Cl Dokumente und Einstellungen The UNIX programming environment htm 28 von 198 20 11 2004 11 29 42 The UNIX programming environment The X window system Because UNIX originated before windowing technology was available the user interface was not designed with windowing in mind The X window system attempts to be like a virtual machine park running a different program in each window Although the programs appear on one screen they may in fact be running on unix systems anywhere in the world with only the output being local to the user s display The standard shell interface is available by running an X client application called xterm which is a graphical front end to the standard UNIX textual interface The xterm program provides a virtual terminal using the X windows graphical user interface It works in exactly the same way as a tty terminal except that standard graphical facilities like copy and paste are available Moreover the user has the convenience of being able to run a different shell in every window For example using the rlogin command it is possible to work on the local system in one window and on another remote system in another window The X window environment allows
117. ferred to by numbers rather than by names stdin File number 0 stdout File number 1 stderr File number 2 The default routes for these files can be changed by redirection The redirection commands are more complicated than in C shell but they are also more flexible Here is a comparison sh csh Description command file command file Stdout to file command 1 file command file Stdout to file command 2 errs No analogue Stderr only to file errs command 1 file 2 gt sl command amp file stdout and stderr to file command 1 file 2 errs No analogue stdout to file stderr to errs Arithmetic in sh Arithmetic is performed entirely by proxy There are no internal arithmetic operators as in the C shell To evaluate an expression we call the expr command or the bc precision calculator Here are some examples of expr a expr Satl increment a a expr 4 10 5 4 10 5 check expr a gt b true 1 false 0 True if a gt Sb file Cl Dokumente und Einstellungen The UNIX programming environment htm 63 von 198 20 11 2004 11 29 42 The UNIX programming environment expr Is very sensitive to spaces and backslash characters Scripts and arguments Scripts are created by making an executable file which begins with the sequence of characters bin sh Although we didn t discuss it before this construction is quite general any executable file which begins with a sequence myprog
118. gandalf local so that it appears in our filesystem at mounted gandalf we would write mount gandalf site gandalf local mounted gandalf The directory mounted gandalf must exist for this to work If it contains files then these files will no longer be visible when the filesystem is mounted on top of it but they are not destroyed Indeed if we then unmount using umount mounted gandalf the spelling is correct then the files will reappear again Some implementations of NFS allow filesystems to be merged at the same mount point so that the user sees a mixture of all the filesystems mounted at the same point Disk device names The convention for naming disk devices in BSD and system 5 unix differs Let us take SCSI disks as an example Under BSD the SCSI disks have names according to the following scheme dev sd0a First partition of disk 0 of the standard disk controller dev sdOb Second partition of disk 0 on the standard disk controller dev sdlc Third partition of disk 1 on the standard disk controller System 5 unix employs a more complex but also more general naming scheme Here is an example from solaris 2 dev dsk c0t3d0s0 Disk controller 0 target disk 3 device 0 segment partition 0 dev dsk cIt1d0s4 Disk controller 1 target disk 1 device 0 segment partition 4 Not all systems distinguish between target and device On many systems you will find only t or d but not both Automating Mounts
119. gram xfig A line drawing figure editor Produces postscript tex and a variety of other output formats xsetroot Load an X bitmap image into the screen root window background Small images are tiled Miscellaneous date Print the date and time ispell Spelling checker xcalc A graphical calculator dc bc Text based calculators xclock A clock ping Send a sonar ping to see if another unix host is alive Terminals In order to communicate with a user a shell needs to have access to a terminal Unix was designed to work with many different kinds of terminals Input output commands in Unix read and write to a virtual terminal In reality a terminal might be a text based Teletype terminal called a tty for short or a graphics based terminal it might be 80 characters wide or it might be wider or narrower Unix take into account these possibility by defining a number of instances of terminals in a more or less object oriented way Each user s terminal has to be configured before cursor based input output will work correctly Normally this is done by choosing one of a number of standard terminal types a list which is supplied by the system In practice the user defines the value of the environment variable TERM to an appropriate name Typical examples are vt 100 and xterm If no standard setup is found the terminal can always be configured manually using UNIX s most cryptic and opaque of commands stty The job o
120. gramming language A make configuration file called Makefile contains rules for how to compile or build other files which make up a program For example the default file knows that in order to go from prog c to prog o the command cc c prog c must be executed The Makefile contains a list of all of the files which compose the program and rules as to how to get to the finished product from the source The idea is that to compile a program we just have to type make make then reads the Makefile and compiles all of the parts which need compiling It does not recompile files which have not changed since the last compilation How does it do this make works by comparing the time stamp on the file it needs to create with the time stamp on the file which is to be compiled If the compiled version is newer than the source the source does not need to be recompiled To make this idea work in practice make has to know how to go through the steps of compiling a program Some default rules are defined in a global configuration file usr include make default mk Let s consider an example of what happens for the the three files a c b c and c c in the example above and let s not worry about what the Makefile looks like yet The first time we compile only the c files exist When we type make the program looks at its rules and finds that it has to make a file called myprog To make this it needs to execut
121. guments in C e Command line arguments in perl Command line arguments in perl e Command line arguments in sh e Command path e Command window e Commands as files e Commands path e Comparison operators in csh e Compiler script e Compilers e Compiling huge programs file Cl Dokumente und Einstellungen The UNIX programming environment htm 184 von 198 20 11 2004 11 29 42 The UNIX programming environment e Compiling programs e connect e continue incsh e Continuing long lines e Copy of output to file e COre e cp command e Creating directories e Creating files e csh e csh e CTRL A e CTRL C e CTRL D e CTRL D and EOF e CTRL E e CTRL L e CTRL e Curses e sur e Cut as a perl script e cut command e Database maps e Database support e date command e Date stamp updating e dbx debugger e Deadlock in NFS Deadlock in NFS e Debugger e Debugger for C e Debugger GUI e Decisions and return codes in sh e delete e Dependencies in Makefiles e Devices e df command e dfstab dfstab e die e Directories creating e Directories deleting e dirent directory interface file Cl Dokumente und Einstellungen The UNIX programming environment htm 185 von 198 20 11 2004 11 29 42 The UNIX programming environment e Disk partition names e Disk usage e DISPLAY variable e Display X e DNS e do while in perl e D
122. h gt KOK KK KK k k k k HH KK KK HH HH KH k ck kc kck ck ck eee eK KK main int pid cid pid getpid printf Fork demo I am the parent pid d n pid Lf i Pork cid getpid printf I am the child cid d of pid d n cid pid ChildProcess exit 0 printf Parent waiting here for the child n wait NULL printf Child finished parent quitting too n ORK KK k k k kk k k KR HK HH Re ee ee ck ck ck ck ck k kc k ck ckckckckckck ck ck kk ChildProcess int i for i 0 i lt 10 i printf M ATI sleep 1 Another possibility is that we might want to execute a program and wait to find out what the result of the program is before continuing There are two ways to do this The first is a variation on the theme above and uses fork file Cl Dokumente und Einstellungen The UNIX programming environment htm 130 von 198 20 11 2004 11 29 42 The UNIX programming environment Let s create a function which runs a shell command from within a C program and determines its return value We make the result a boolean integer value so that the function returns true if the shell command exits normally See section Return codes if ShellCommandReturnsZero shell command printf Command s went ok n shell command To do this we first have to fork a new process and then use one of the exec commands to load a new code image on top of the new
123. hat it is as immediate as shell programming If you are inexperienced Perl is a little easier than C because many features are ready programmed into the language but with time one also builds up a repertoire of C functions which can do the same tricks Exercises 1 Write a progam which prints out all of its arguments alphabetically together with the first and the last and the number of arguments 2 Write a program which prints out the pathname of the home directory for a given user The file Cl Dokumente und Einstellungen The UNIX programming environment htm 101 von 198 20 11 2004 11 29 42 The UNIX programming environment user s login name should be given as an argument 3 Write a program called search replace which looks for a given string in a list of files and replaces it with a new string You should be able to specify a list of files using ordinary unix wildcards e g search replace search string replace string text This is a dangerous operation What if the user types the strings incorrectly How can you may the program safer 4 Write a program which opens a pipe from ps and computes the total cpu time used by each user Print the results in order of maximum to minimum Hint use an associated array to store the information 5 Write a program which forks and goes into the background Make the program send you mail when some other user of your choice logs in Use sleep to check only every few minutes 6 Open a pip
124. he display will always have access to the magic cookie and will therefore always be able to open windows on the display Other users must obtain a copy of the file in order to open windows there The command xauth is an interactive utility used for controlling the contents of the Xauthority file See the xautn manual page for more information Multiple screens The window paradigm has been very successful in many ways but anyone who has used a window system knows that the screen is simply not big enough for all the windows one would like Unix has several solutions to this problem One solution is to attach several physical screens to a terminal The X window system can support any number of physical screens of different types A graphical designer might want a high resolution colour screen for drawing and a black and white screen for writing text for instance The disadvantage with this method is the cost of the hardware A cheaper solution is to use a window manager such as fwvm which creates a virtual screen of unlimited size on a single monitor As the mouse pointer reaches the edge of the true screen the window manager replaces the display with a new blank screen in which to place windows A miniaturized image of the windows on a control panel acts as a map which makes it possible to find the applications on the virtual screen Yet another possibility is to create virtual displays inside a single window In other words one can
125. he purpose of this is to ensure that nobody has the right to read or write files unless they are opened very explicitly by the user who owns them In order for files to be readable on the WWW they must have file mode 644 and they must lie file Cl Dokumente und Einstellungen The UNIX programming environment htm 102 von 198 20 11 2004 11 29 42 The UNIX programming environment in a directory which has mode 755 In order for a CGI program to be executable it must have permission 755 and in order for such a program to write to a file in a user s directory it must be possible for the file to be created if necessary and everyone must be able to write to it That means that files which are written to by the WWW must have mode 666 and must either exist already or lie in a directory with permission 777 6 Protocols CGI script programs communicate with W3 browsers using a very simple protocol It goes like this e A web page sends data to a script using the forms interface Those data are concatenated into a single line The data in separate fields of a form are separated by amp signs New lines are replaced by the text 0D0 0A which is the DOS ASCII representation of a newline and spaces are replaced by symbols e A CGI script reads this single line of text on the standard input e The CGI script replies to the web browser The first line of the reply must be a line which is tells the browser what mime type
126. his is through regular expressions Regular expressions are used by the egrep utility text editors like ed vi and emacs and sed and awk They are also used in the C programming language for matching input as well as in the Perl programming language and 1ex tokenizer Here are some examples using the egrep command which print lines from the file etc rc which match certain conditions The contruction is part of egrep Everything in between these symbols is a regular expression Notice that special shell symbols amp have to be preceded with a backslash in order to prevent the shell from expanding them Print all lines beginning with a comment egrep 54 etc re Print all lines which DON T begin with 4 file Cl Dokumente und Einstellungen The UNIX programming environment htm 19 von 198 20 11 2004 11 29 42 The UNIX programming environment egrep etc rc Print all lines beginning with e f or g egrep efg etc rc Print all lines beginning with uppercase egrep L A 2 etc rc Print all lines NOT beginning with uppercase egrep A 27 etc re Print all lines containing amp egrep Cep AW etc rc All lines containing amp but not starting egrep amp etc rc Regular expressions are made up of the following atoms These examples assume that the file etc rc exists If it doesn t exist on the machine you are using try to find the equivalent by for i
127. host See http www iu hioslo no mark cfengine file Cl Dokumente und Einstellungen The UNIX programming environment htm 165 von 198 20 11 2004 11 29 42 The UNIX programming environment Summary There are many topics which we could have covered in this chapter but to cover any more would justify a whole book on the subject of system administration Summary of programming idioms True and false C shell True non zero non empty value False zero or null string i Bourne shell True 0 returned by shell command False non zero returned by shell command Note that test converts from C shell style to Bourne shell Perl True non zero non empty value False zero or null string dq ow True non zero integer False zero integer Input from tty f C shell lt Bourne shell line read Perl lt STDIN gt Pe ey file Cl Dokumente und Einstellungen The UNIX programming environment htm 166 von 198 20 11 2004 11 29 42 The UNIX programming environment scanf Redirection of I O f C shell command gt file command gt amp file command gt gt file commandi command2 Bourne shell command gt file command gt file 2 gt amp 1 command gt gt file commandi command2 Perl open HANDLE gt file open HANDLE gt file 2 gt amp 1 open HANDLE gt gt file open HANDLE commandl1 open HANDLE command2 nao ropen rfile w
128. ines on a network which have not been correctly configured There could be enough right that they actually manage to talk to the network but not everything would work as intented Again a simple script would do the job of checking that the values were correct ifconfig will print its configuration given the command ifconfig le0 The ethernet interface has different names on different unices leO Sun SunOS Solaris InO Digital Ultrix osf1 lanO HPUX end AIX IBM ecO IRIX cfengine who needs a script Although it is possible to write scripts to automate and check many of the procedures above a general tool would be a much better idea cfengine is a very high level description language which allows the system administrator to configure an entire network from a simple descriptive file cfengine uses classes to identify the needs of individual machines Thus we sould define actions to be carried out for all systems which ran AIX or all workstations in the faculty of medicine or all the machines which are both servers and run HPUX etc cfengine takes care of links mount operations interface configuration nameserver designation controlled script execution and a number of other tasks It performs substantial checking on each link it makes without the need for any user code and most importantly its use of class abstractions reduces the number of tests which have to be made to determine the correct configuration for each
129. ing the data 2 Next scan through the kernel to the offset proc which is where the table of addresses starts and read the address of the actual structure a We then read the procedure table to get the actual structure file Cl Dokumente und Einstellungen The UNIX programming environment htm 140 von 198 20 11 2004 11 29 42 The UNIX programming environment 4 Now step through the pointer table from the base address in proc table and increment by adding an offset to the base value 5 If defined 6 Don t really want to see 50 copies of the swapper 7 This is pure hacking With a lot of detective work and a bit of patience we find the relevant information in the kernel There is a lot of cross referencing in the Structures and many multiply linked lists so that the info is buried just about as deep as it could possibly be The important files are usr include sys proc h where proc is defined usr include sys pstat h where pst status is defined note the member in proc which is called p upreg is NOT of the latter type although in Top 3 0 this is used In fact most of the info is in this sub structure so that the tens of members in the main proc structure are irrelevant Note that the command name is in this substructure lucky if you find it NOTE that the system calls here are not supported There is no supported way of reading the kernel data structures Su end smallexample De
130. ions on files e Permissions determining in C e pico e Picture processing e pine mailer e e I o 1pes e Pipes in C e Piping to more to prevent scrolling e popen e Portmapper e POSIX standard e Postscript viewers e Printer queue e Printer status e PRINTER variable e Printing a file e Printing multiple lines e Procedures and subroutines in sh e Process moving to background e Processes e Prompt redefining e Protecting files from overwrite with e Protection bits e ps command e Quotas file Cl Dokumente und Einstellungen The UNIX programming environment htm 192 von 198 20 11 2004 11 29 42 The UNIX programming environment e readdir command e readlink e reboot command e recv e Redefining list separator in sh e Redirecting stdio in sh e Redirection of stdio e Regular expressions e Reliable socket protocol e Renaming files e repeat e Result of a command into a string e Return codes e rlogin e rlogin program e rm command e rmail in emacs e rmdir command e Role of C in unix e Root privileges e root user e RPC e rpcgen e rpcinfo e rsnh e s bit s bit e Scalar variables in perl e scheme e Screen e Screens e Script aliases in W3 e Script making e Scripts in sh making e Searching and replacing in perl example e sed as a perl script e sed batch editor e sed editor e
131. is gives C programmers access to the shell s global environment Environment variables in C In addition to the envp vector it is possible to access the environment variables through the call getenv This is used as follows suppose we want to access the shell environment variable HOME char string string getenv HOME string is now a pointer to static but public data You should not use string as if it were you re own property because it will be used again by the system Copy it s contents to another string before using the data char buffer 500 strcpy burrer strring Text parsing tools lex and yacc This section is a taster only You only need to know what lex and yacc are not how they work lex and yacc are two tools for the C programmer who wishes to make a text parser A text file Cl Dokumente und Einstellungen The UNIX programming environment htm 122 von 198 20 11 2004 11 29 42 The UNIX programming environment parser is a program which reads a text file and interprets the symbols in it Every programming language must include a text parser for instance The yacc yet another compiler compiler program generates C code which parses a textfile given a description of the syntax rules for the file In other words we define the logical structure of the text file according to the way we wish to interpret it and give the rules to yacc yacc produces C code from this whi
132. it will never do because it is waiting for B The solution to this dilemma is to use the bg option and the intr option intr means that it is possible to abort the mount operation with a CTRL C bg means that once if the connection times out mount continues trying to mount the server in the background but the A doesn t wait for B Unfortunately the background option is not the default so it helps to know this in advance If necessary the deadlock can be broken by booting in single user mode no filesystems except and usr and editing the filesystem table exports or share In order to be able to mount a filesystem we must grant permission to others on the host to which the disk is physically attached We say that the host must export the filesystem so that others can use it Exporting a filesystem means adding the name of our system to a list of allowed hosts for each filesystem we want to mount The file is called etc exports on most implementations Under solaris it is called etc d s dfstab The format of the file varies enormously between different versions of unix but the general format is somthing like this usr access boson fermion semion anyon export exec kvm sun4c sunos 4 1 3 export root boson access boson root boson export swap2 boson access boson root boson export root fermion access fermion root fermion export swap2 fermion access fermion root fermion export root semion
133. ite operations can use When a read write operation is directed at an NFS filehandle an nfsd daemon at the server end is scheduled to handle the request Note the NFS code resides entirely in the system kernel The nfsd daemons are only wrapper programs for NFS system calls They exist because the servers need to be multithreaded in order to handle multiple requests Most kernels are not multithreaded so this is simulated by making daemons independent processes which are then scheduled as heavyweight processes by the kernel The effect is to multithread the kernel system calls file Cl Dokumente und Einstellungen The UNIX programming environment htm 156 von 198 20 11 2004 11 29 42 The UNIX programming environment C support for NFS The support for NFS mounting in the standard C library is through two sources NFS is based on the Sun s RPC system so the basic calls are only instances of standard RPC protocols The C functions in the standard input output library can be used to access NFS filesystems Since NFS imitates the UNIX filesystem as closely as possible NFS filesystems can be mounted in exactly the same way as ordinary filesystems Unfortunately the C functions which perform the mount operation in UNIX and depressingly non standard They differ on almost every implementation of UNIX The basic function which mounts a filesystem in mount seeman 2 mount The mount table is stored in a file etc mtab on BSD systems again
134. ition subtraction and multiplication etc To tell the C shell that you want to perform an operation on numbers rather than strings you use the symbol followed by a space Then the following operations are possible var 45 Assign a numerical value to var file Cl Dokumente und Einstellungen The UNIX programming environment htm 57 von 198 20 11 2004 11 29 42 The UNIX programming environment echo var Print the value var Svar 34 Add 34 to var var 34 Add 34 to var var 1 subtract 1 from var var 5 Multiply var by 5 i var 3 Divide var by 3 integer division var 3 Remainder after dividing var by 3 a var Increment var by 1 var Decrement var by 1 array 1 5 Numerical array logic x gt 6 amp amp x lt 10 AND logic x gt 6 x 10 4 OR false Svar Logical NOT bits x Sy Bitwise OR bits x Sy Bitwise XOR bits Sx amp Sy Bitwise AND shifted Svar gt gt 2 Bitwise shift right back Svar lt lt 2 Bitwise shift left These operators are precisely those found in the C programming language Examples The following script uses the operators in the last two sections to take a list of files with a given file extension say doc and change it for another say tex This is a partial solution to the limitation of not being able to do multiple renames i
135. ive array for every program called 3ENV This contains the environment variables defined in the parent shell which is running the Perl program For example file Cl Dokumente und Einstellungen The UNIX programming environment htm 79 von 198 20 11 2004 11 29 42 The UNIX programming environment print Username SENV USER n Sld LD_LIBRARY_PATH print The link editor path is SENV ld n To get the current path into an ordinary array one could write path_array split SENV PATH Array example program Here is an example which prints out a list of files in a specified directory in order of their UNIX protection bits The east protected file files come first local bin perl Demonstration of arrays and associated arrays Print out a list of files sorted by protection so that the least secure files come first e g arrays lt list of words gt arrays C HEE HH HH Ht HE EH HE EH HH TE EE EE EE EH EE EE EH HE EE EE EE EE EE EE HH 2 print You typed in ARGV 1 arguments to command n if S ARGV lt 1 print That s not enough to do anything with n Jj while next arg shift ARGV if I f Snext arg d next arg print No such file next_arg n next Sdev ino Smode Snlink Suid gid rdev size stat next_arg Soctalmode sprintf o Smode amp 0777 Sassoc_array Soctalmode next arg size Ssize
136. k ee ko kok ok k X X X ck ck ck ck ck kk ck ck ck ckck ck ckckckck ck kk Main KK KK k HH X k k k kk k eee kok ok k X X X ck ck ck kc k kc kc k ck ck ckck ck ckckckck ck kk main argc argv file Cl Dokumente und Einstellungen The UNIX programming environment htm 136 von 198 20 11 2004 11 29 42 The UNIX programming environment int argc char argv CheckOptions argc argv Enit ReadTable ORK KKK k k k kk HH KK Re oko ee kk ck ck ck ck ck Ck Ck kc k ck ck ck HK kk Level 1 x ORK KKK HH k k KH HK ee ee HH ck ck ck ck Ck kc kck ee ee ek KK KK CheckOptions argc argv Uses GLOBAL flags int argc char argv i inb us for 2 15 1 argo i keV boj bunte ea ee a 1 0 AUX 1 KOR KK k k k HH HH kk HK HH HH ck ck ck kc k kc kc k ck ckck ck ckckckckock kk kk Init UID getuid who is running this if nlist VMUNIX nl lt 0 perror nlist procedure table exit 1 ORK KK k k k HH X k kk HK ee ee HH ck ck ck k ck Ck Ck ck ck ckck ck ckckckck ck kk kk ReadTable file Cl Dokumente und Einstellungen The UNIX programming environment htm 137 von 198 20 11 2004 11 29 42 The UNIX programming environment int offset nproc int already seen swapper 0 long pt addr struct proc proc table p Struct pst status pstatus if kmem open dev kmem O RDONLY lt 0 perror open dev kmem exit 1
137. l print Content type text html n n Get the data from the form Sinput lt STDIN gt and echo them back print input n n n Sinput s g Now split the lines and convert array split amp Sinput foreach Svar array print var n file Cl Dokumente und Einstellungen The UNIX programming environment htm 106 von 198 20 11 2004 11 29 42 The UNIX programming environment print Done Mn We now have a series of elements in our array The output from this script is something like this variablel Mark Burgess variable2 0D 0AI just called to say wrap SODSOA heytpigS2Ct nothing 27stworkingtout thetwaytiIt planned variablel Mark Burgess variable2 2 0D 0AI just called to say wrap 0D 0A hey pig 2Cnothing 27s working out the way I planned Done As you can see all control characters are converted into the form xx We should now try to do something with these Since we are usually not interested in keeping new lines or any other control codes we can simply null out these with a line of the form Sinput s g The regular expression matches anything beginning with a percent symbol followed by two characters The resulting output is then free of these symbols We can then separate the variable contents from their names by splitting the input Here is the complete code local bin perl Reply with proper protocol
138. le lpg lpstat Show the status of the print queue File browsing file Cl Dokumente und Einstellungen The UNIX programming environment htm 23 von 198 20 11 2004 11 29 42 The UNIX programming environment more Shows one screen full at a time Possibility to search for a string and edit the file This is like type file more in DOS less An enhanced version of more Midnight commander a free version of the Norton Commander PC utility for unix Only for non serious UNIX users fmgr A window based file manager with icons and all that nonsense Ownership and granting access permission chmod Change file access mode chown chgrp Change owner and group of a file The GNU version of chown allows both these operations to be performed together using the syntax chown owner group file acl On newer Unices Access control lists allow access to be granted on a per user basis rather than by groups Extracting from and rebuilding files cut Extract a column in a table paste Merge several files so that each file becomes a column in a table sed A batch text editor for searching replacing and selecting text without human intervention awk A prerunner to the Perl language for extracting and modifying textfiles rmcr Strip carriage return ASCII 13 characters from a file Useful for converting DOS files to unix Locating files find Search for files from a specified directory using various criteria locate Fast s
139. line manual pages For instance suppose you do not remember how to create a new directory you could do the following nexus man k dir dir ls 1 list contents of directories dirname dirname 1 strip non directory suffix from file name dirs bash 1 bash built in commands see bash l1 find find 1 search for files in a directory hierarchy ls ls 1 list contents of directories mkdir mkdir 1 make directories pwd pwd 1 print name of current working directory rmdir rmdir 1 remove empty directories The man k command looks for a keyword in the manual and lists all the references it finds The command apropos is completely equivalent to man k Having discovered that the command to create a directory is mkdir you can now look up the specific manaul page on mkdir to find out how to use it man mkdir Some but no all of the UNIX commands also have a help option which is activated with the n or help command line option file Cl Dokumente und Einstellungen The UNIX programming environment htm 5 von 198 20 11 2004 11 29 41 The UNIX programming environment dax mkdir help Usage mkdir OPTION DIRECTORY Es parents no error if existing make parent directories as needed m mode MODE set permission mode as in chmod not 0777 umask help display this help and exit version output version information and exit dax NEVER DO s in UNIX There are some things that y
140. line starting with hash symbol first char regex n match line ending in a semi colon Try running this program with the test data on the following file which is called regex_test in the example program A line beginning with a hash symbol file Cl Dokumente und Einstellungen The UNIX programming environment htm 96 von 198 20 11 2004 11 29 42 The UNIX programming environment JUST UPPERCASE LETTERS just lowercase letters Letters and numbers 123456 123456 A line ending with a semi colon Line with a comment COMMENT Example convert mail to WWW pages Here is an example program which you could use to automatically turn a mail message of the form From Newswire To Mailzhtml Subject Nothing happened On the 13th February at kl 09 30 nothing happened No footprints were found leading to the scene of a terrible murder no evidence of a struggle etc etc into an html file for the world wide web The program works by extracting the message body and subject from the mail and writing html commands around these to make a web page The subject field of the mail becomes the title The other headers get skipped since the script searches for lines containing the sequence colon space or A regular expression is used for this local bin perl Make HTML from mail m BeginWebPage ReadNewMail EndWebPage m m Hit HE HE Ht k FE FE aE E FE E HE HE E FE HE FE FE FE AEE SHE
141. ls started by the current shell while global variables are inherited by all sub shells The Bourne shell and the C shell use these conventions differently and not always consistently You will see how to define these below For now you just have to know that you can use the following commands from the C shell to list these variables The command env can be used in either C shell or Bourne shell to see all of the defined environment variables Wildcards Sometimes you want to be able to refer to several files in one go For instance you might want to copy all files ending in c to a new directory To do this one uses wildcards Wildcards are characters like which stand for any character or group of characters In card games the joker is a wild card which can be substituted for any other card Use of wildcards is also called filename substitution in the unix manuals in the sections on sh and csh The wildcard symbols are Match any number of characters e g 1s etc rc usus Match any character in a list enclosed by these brackets e g 1s abc C Here are some examples and explanations ebelrg v299 Match all files in etc whose first three characters are rc and are 7 characters long re Match all files ending in c i e all C programs ea nc List all files ending on c or C i e all C and C programs a z Match any file ending in a b c up to z etc file Cl Dokumente und Einstellungen
142. lt p gt n print TMP Smessage print TMP n lt hr gt n file Cl Dokumente und Einstellungen The UNIX programming environment htm 109 von 198 20 11 2004 11 29 42 The UNIX programming environment print TMP line close PAGE close TMP if rename tmp page guestbook page print Oops Rename operation failed n chmod 0666 Sguestbook page This script works by reading through the old guest book file opening a new copy of the guest book file and appending a new messages at the end The end of the message section not counting the lt HTML gt tags is marked by a comment line gl LAST ENTRY gt Note that a provisional guest book file has to exist in the first place The script writes to a new file and then swaps the new file for the old one The guest book file looks something like this lt html gt lt head gt lt title gt Comments lt title gt lt head gt lt body gt lt h1 gt My guest book lt h1 gt lt b gt Entry no Wednesday Feb 28 1996 from host dax lt b gt lt p gt From Mark Burgess iu hioslo no lt p gt Just to start the ball rolling lt hr gt lt b gt Entry no Tuesday Mar 26 1996 from host enterprise subspace net lt b gt lt p gt From spock enterprise lt p gt Registering a form of energy never before encountered lt LAST ENTRY gt lt body gt lt address gt lt a href http www iu hioslo no mark gt Mark
143. luding stderr a Append ignoring noclobber sagt Append stdout stderr ignore noclobber we See below The last of these commands reads from the standard input until it finds a line which contains a word It then feeds all of this input into the program concerned For example nexus mail mark lt lt quit nexus 1 Hello mark nexus 2 Nothing much to say nexus 2 so bye nexus 2 nexus 2 quit Sending mail Mail sent The mail message contains all the lines up to but not including marker This method can also be used to print text verbatim from a file without using multiple echo commands Inside a script one may write cat marker MENU 1 choice 1 2 choice 2 marker The cat command writes directly to stdout and the input is redirected and taken directly from the script file A very useful construction is the pipe facility Using the symbol one can feed the stdout of one program straight into the stdin of another program Similarly with amp both stdout and stderr can be piped into the input of another program This is very convenient For instance look up the following commands in the manual and try them ps aux more echo Keep on sharpenin them there knives mail henry vmstat 1 head ls l etc tail Note that when piping both standard input and standard error to another program the two files do file Cl Dokumente und Einst
144. m in a special way A signal handler is made by calling the function signal for each signal and by specifying a pointer to a function which will be called in the event of a signal For example main file Cl Dokumente und Einstellungen The UNIX programming environment htm 134 von 198 20 11 2004 11 29 42 The UNIX programming environment int HandleSignal signal SIGTERM HandleSignal HandleSignal Tidy up and exit cleanly exit 0 SIGTERM is the usual signal sent by the command ki11 There are many other signals which can be sent to programs Here is list You have to decide for yourself whether or not you want to provide your own signal handling function To ignore a signal you write signal SIGtype SIG_IGN To remove a signal handler and re activate a signal you write signal SIGtype SIG_DFL Difficult example Process table Skip this section unless you are very interested The ps command under system 5 UNIX is somewhat different to that in BSD Here is an example of reading the kernel process table on a HPUX machine The output is listed BSD style VRR Ck k kk X k kkokokok kok k k X X ck ck ck ck ck ck kc k ck ck ckckckckckck ck k kk ur mps module for HP UX machines 9000 series ul d gt This program must be run setuid root in order to read ur the kernel memory device dev kmem ur See notes at end of program Hint make the wi
145. mand path would have to be set differently for each type of machine Defining variables with set setenv We have already seen in the examples above how to define variables in C shell Let s formalize this To define a local variable that is one which will not get passed on to programs and sub shells running under the current shell we write set local some string file Cl Dokumente und Einstellungen The UNIX programming environment htm 38 von 198 20 11 2004 11 29 42 The UNIX programming environment set myname whoami These variables are then referred to by using the dollar symbol i e The value of the variable local Is Slocal echo local myname Global variables that is variables which all sub shells inherit from the current shell are defined using setenv setenv GLOBAL Some other string setenv MYNAME who am i Their values are also referred to using the symbol Notice that set uses an sign while setenv does not Variables can be also created without a value The shell uses this method to switch on and off certain features using variables like noclobber and noglob For instance nexus set flag nexus if flag echo Flag is set Flag is set nexus unset flag nexus if flag echo Flag is set nexus The operator variable is true if variable exists and false if it does not It does not matter whether the variable holds any information
146. mon parent If we kill a parent then unless the child has detached itself from the parent all of its children die too If a child dies the parent is not affected Sometimes when a child is killed it does not die but becomes defunct or a zombie process This means that the child has a parent which is waiting for it to finish If the parent has not yet been informed that the child has died for example because it has been suspended itself then the dead child is not removed from the kernel s process table When the parent wakes up and receives the message that the child has terminated the process entry for the dead child can be removed Y N C shell builtins jobs kill fg bq breakkey Now let s look at some commands which are built into the C shell for starting and stopping processes C shell refers to user programs as jobs rather than processes but there is no real file Cl Dokumente und Einstellungen The UNIX programming environment htm 47 von 198 20 11 2004 11 29 42 The UNIX programming environment difference The added bonus of the C shell is that each shell has a job number in addition to its PID The job numbers are simpler and are private for the shell whereas the PIDs are assigned by the kernel and are often very large numbers which are difficult to to remember When a command is executed in the shell it is assigned a job number If you never run any background jobs then there is only ever one job number 1 si
147. n command can be used to execute UNIX programs and get the result into a Perl variable file Cl Dokumente und Einstellungen The UNIX programming environment htm 75 von 198 20 11 2004 11 29 42 The UNIX programming environment Here is a simple structured hello world program in Perl Notice that subroutines are called using the amp symbol There is no special way of marking the main program it is simply that part of the program which starts at line 1 local bin perl Comments amp Hello amp World end of main sub Hello print Hello sub World print World n The parentheses on subroutines are optional if there are no parameters passed Notice that each line must end in a semi colon Perl variables Scalar variables In Perl variables do not have to be declared before they are used Whenever you use a new symbol Perl automatically adds the symbol to its symbol table and initializes the variable to the empty string It is important to understand that there is no practical difference between zero and the empty string in perl except in the way that you the user choose to use it Perl makes no distinction between strings and integers or any other types of data except when it wants to interpret them For instance to compare two variables as strings is not the same as comparing them as integers even if the string contains a textual representation of an integer Take a look
148. n read the value of a variable using the read command with syntax read variable This reads in a string from the keyboard and terminates on a newline character Another way to do this is to use the input command to access a particular logical device The keyboard device in the current terminal is dev tty so that one writes variable line lt dev tty which fetches a single line from the user Here are some examples of these commands First a program which asks yes or no bin sh it Yes or no echo Please answer yes or no file Cl Dokumente und Einstellungen The UNIX programming environment htm 67 von 198 20 11 2004 11 29 42 The UNIX programming environment answer line dev tty case Sanswer in ve qo wm 17 ape 3 echo YES n N echo NO echo Can t you answer a simple question esac echo The end Notice the use of pattern matching and the OR symbol bin sh Kernel check if test f vmunix Check that the kernel is there then echo This is not BSD unix hmmm if T f Zhp u then echo It s a Hewlett Packard machine fi elif w vmunix then echo HEY The kernel is writable my me else echo The kernel is write protected echo The system is safe from me today fi Loops in sh The loop structures in the Bourne shell have the following syntax while unix command d commands done The first command will most lik
149. n shell bin csh f HEH HE HEH HH HH HE EH HH HE EH HH HE EE EE EH HH HH EE EE EE OEE m Change file extension for multiple files HEH HHH HH HH HE EH HH HE HEH HH EEE EE HH HH EEE EH EE EEE EE 2 5 if S argv lt 2 then echo Syntax chext oldpattern newextension echo e g chext doc tex exit 0 endif file Cl Dokumente und Einstellungen The UNIX programming environment htm 58 von 198 20 11 2004 11 29 42 The UNIX programming environment mkdir tmp chext Suser Make a scratch area set newext Sargv S argv Last arg is new ext set oldext argv 1 e echo Old extenstion was Soldext echo New extension newext okay y n switch lt case y breaksw default echo Nothing done exit 0 endsw HH HHH HH HH HE HE EH EH EH EE HE EE EE EE EE EH EH EE HE HE EH EE HE HE EZ Remove the last file extension from files Hee HEH EH HH HE HE EH EH EH EE EEE EE EH EE EE EE EH EE HE HE EH EE HE 4439494343953 16 foreach file argv i if i fargv break cp file tmp chext user file r temporary store end E L L L L L L Ht EH L L U HE HE HF Add newext file extension to files Ht HH HH HH HH HE HE EH EH EH EE HE EH EH EE EE EH EH L EE HE L HH HE EH EE HE Ht EHF set array ls tmp chext user foreach file Sarray if f Sfile newext then echo destination file file newext exists No action taken continue endif cp tmp chext S user S file Sfil
150. name coded pwd Suid gid x Sy z Sgcos Shome shell getpwnam SENV USER if crypt Soldpwd coded_pwd ne Scoded_pwd print nPasswd incorrect n exit 1 Soldpwd Destroy the evidence print nNew passwd Snewpwd lt STDIN gt print nRepeat new passwd Srnewpwd lt STDIN gt file Cl Dokumente und Einstellungen The UNIX programming environment htm 89 von 198 20 11 2004 11 29 42 The UNIX programming environment chop newpwd chop rnewpwd if Snewpwd ne Srnewpwd print n Incorrectly typed Password unchanged n exit 1 Ssalt rand Snew_coded_pwd crypt Snewpwd Ssalt print AnWMn name new coded pwd uid gid gcos home shell Nn Example with fork The following example uses the fork function to start a daemon which goes into the background and watches the system to which process is using the greatest amount of CPU time each minute A pipe is opened from the BSD ps command local bin perl A fork demo This program will sit in the background and make a list of the process which uses the maximum CPU average at 1 minute intervals On a quiet BSD like system this will normally be the swapper long term scheduler dE db db db db ok Strue 1 Slogfile perl cpu logfile print Max CPU logfile forking daemon n if fork exit 0 while Strue open logfile gt gt Slogfile die Can t o
151. nce every job exits before the next one starts However if you run background tasks then you can have several jobs active at any time Moreover by suspending jobs C shell allows you to have several interactive programs running on the same terminal the g and bg commands allow you to move commands from the background to the foreground and vice versa Take a look at the following shell session nexus emacs myfile amp 1 4990 nexus other commands edit myfile and close emacs 1 Exit 70 emacs myfile When a background job is done the shell prints a message at a suitable moment between prompts 1 Done emacs myfile This tells you that job number 1 finished normally If the job exits abnormally then the word Done may be replaced by some other message For instance if you kill the job it will say unix kill 12 12 Terminated textedit file You can list the jobs you have running using the jobs command The output looks something like 1 Running textedit c tex 3 Running textedit glossary tex 4 Running textedit net tex 5 Running textedit overview tex 6 Running textedit perl tex 7 Running textedit shell tex 8 Running textedit sysadm tex 9 Running textedit unix tex 10 Running textedit xll tex 11 Running shelltool 15 Suspended emacs myfile To suspend a program which you are running in the foreground you can type CTRL z this is like sending a kill
152. ndow a bit 7 wider this is WIDE SCREEN ENTERTAINMENT 57 d OK KK k k k k k k k k k HH kk kCkCKCkCkc kc kCkCkckckckckck ck ck ck ck ck ck kc kc kck ck ckckckckck ck k kk include lt stdio h gt include lt sys param h gt include lt fcntl h gt file Cl Dokumente und Einstellungen The UNIX programming environment htm 135 von 198 20 11 2004 11 29 42 The UNIX programming environment include lt sys proc h gt finclude lt sys pstat h gt include lt pwd h gt include mps h ifdef hp9000s800 include lt nlist h gt endif OK KK k k HH HK Ke oko ee HH KH RR eee ee eK ck kk struct nlist nl setup for calls to nlist 3 ifdef hp9000s800 LOCI NEEOON E entries in process table p roe pointer to process table else Dot mproo Fy entries in process table _proc pointer to process table endif mw nlist structures differ from OS to OS but two symbols are always present namely n value and n type These are the ones we need fortunately n define C NPROC 0 indices into the above array define C PROC 1 OK KK k k k kk k k k k HH KH KR eee ee ck ck ck ck ck ck Ck Ck ck ck ck ckck KK KK define VMUNIX hp ux define ROOT 0 int kmem int AUX 0 int UID double FSCALE 0 01 This should really be read from the kernel but never mind M ORK KKK k k kk k k k kok ee ee k X X k k kk kk
153. ng If the result is different from zero then we know that all of the bits were also set in the mode string As in C the bitwise AND operator in perl is called amp For example to test whether a file is writable to other users in the same group as the file we would write the following Smask 020 Leading 0 means octal number Sdevice Sinode Smode stat file if Smode amp Smask print File is writable by the group n file Cl Dokumente und Einstellungen The UNIX programming environment htm 88 von 198 20 11 2004 11 29 42 The UNIX programming environment Here the 2 in the second octal number means write the fact that it is the second octal number from the right means that it refers to group Thus the result of the if test is only true if that particular bit is true We shall see this idiom in action below Perl example programs The passwd program and crypt function Here is a simple implementation of the UNIX passwd program in Perl local bin perl A perl version of the passwd program Note the real passwd program needs to be much more secure than this one This is just to demonstrate the use of the crypt function Hit tt Ht HH HH EH EE EH HH HH HH HH EE EH HH FE TE EE EH EE E E E E E E E EEE E 25 print Changing passwd for SENV USER on SENV HOST n system stty echo print Old passwd Soldpwd lt STDIN gt chop Soldpwd S
154. ng for missing libraries which you want to include in your environment variable Lb LIBRARY PATH Searching the enire disk from the root directory could take a long time so it pays to run this in the background If we want to see what processes are running we can use the ps command ps without any file Cl Dokumente und Einstellungen The UNIX programming environment htm 45 von 198 20 11 2004 11 29 42 The UNIX programming environment arguments lists all of your processes i e all processes owned by the user name you logged in with ps takes many options for instance ps auxg will list all processes in gruesome detail The g is for group not gruesome ps reads the kernel s process tables directly Processes can be stopped and started or killed one and for all The ki11 command does this There are in fact two versions of the k111 command One of them is built into the C shell and the other is not If you use the C shell then you will never care about the difference We shall nonetheless mention the special features of the C shell built ins below The kill command takes a number called a signal as an argument and another number called the process identifier or PID for short Kill send signals to processes Some of these are fatal and some are for information only The two commands kill 15 127 kill 127 are identical They both send signal 15 to PID 127 This is the normal termination signal and it is of
155. nstance replacing etc rc with etc rc which will try to find a match beginning with the rc Match any single character except the end of line Match the beginning of a line as the first character TT Match end of line as last character 7 Level Match any character in the list between the square brackets see below NEN Match zero or more occurrances of the preceding expression i Match one or more occurrences of the preceding expression Match zero or one occurrance of the preceding expression You can find a complete list in the unix manual pages The square brackets above are used to define a class of characters to be matched Here are some examples e f the square brackets contain a list of characters a z156 then a single occurrance of file Cl Dokumente und Einstellungen The UNIX programming environment htm 20 von 198 20 11 2004 11 29 42 The UNIX programming environment any character in the list will match the regular expression in this case any lowercase letter or the numbers 1 5 and 6 e If the first character in the brackets is the caret symbol in the list will be matched e Normally a dash or minus sign means a range of characters If it is the first character after the or after then it is treated literally gt then any character except those Nested shell commands and The backwards apostrophes can be used in all shells and also in the programming language Perl When these a
156. nt Recently several unix vendors have stopped including the C compiler as a part of the system in order to charge extra but there is a public domain version of the compiler called gcc for GNU C so we shall use this in the examples To compile a program consisting of several files of code we first compile all of the separate pieces without trying to link them There are therefore two stages first we turn c files into o files This compiles code but does not fix any address references Then we link all o files into the final executable including any libraries which are used Let s suppose we have files a c b c and c c We write file Cl Dokumente und Einstellungen The UNIX programming environment htm 113 von 198 20 11 2004 11 29 42 The UNIX programming environment gcc G AG D G G C This creates files a o b o and c o Next we link them into one file called myprog gcc o myprog a o b o c o If the naming option o myprog is not used the link 1d uses the default name a out for the executable file Libraries and LD LIBRARY PATH The resulting file is called myprog and includes references only to the standard library 1ibc If we wish to link in the math library 1ibm or the cursor movement library 1ibcurses orin general a library called 1ibBLAH we need to use the 1 directive gcc o myprog files o lm lcurses 1BLAH The compiler looks for a suitable library in all
157. nt hrs mins if p NULL Empty pointer TA return if AUX amp amp p gt pst_uid UID Only want the users processes return pw getpwuid uid_t p gt pst_uid get the users real name ar d hrs int p gt pst cptickstotal 3600 mins int p gt pst cptickstotal 3600 60 if p gt pst nice gt 10 BSD nice notation actually not that nice Xf status 2 N else if p gt pst nice lt 10 file Cl Dokumente und Einstellungen The UNIX programming environment htm 139 von 198 20 11 2004 11 29 42 The UNIX programming environment status 2 switch p 2pst Stat Try to give some BSD status info 2 case PS SLEEP status 0 S break case PS RUN status 0 R break case PS STOP status 0 T break case PS ZOMBIE status 0 Z break case PS IDLE status 0 I break default status 0 break oe printf 8s 0d 5 2f 6d 4s 2 2d 2 2q sXn pw gt pw name pP 2pst pid double p gt pst pctcpu 100 0 p gt pst_rssize status hrs mins p gt pst cma KOK KK k k kk k k kk k HH kk kk k k eee kok HH ck ck k Ck kc k kc kc kc k ck ck KK ck ck 1 scan through the kernel memory using the list of addresses we retrieved using nlist We want the value of nproc ie the number of processes in the process table It s just an integer Now use calloc to allocate an array for stor
158. ntation latex man latex man The Makefile above can be invoked in several ways ke cfengine clean install tar documentation K O a a ak ak a a DO O0 K O Hu Beg K O If we simple type make i e the first of these choices make takes the first of the rules it finds as the object to build In this case the rule is cfengine so the first two forms above are equivalent On the other hand if we type file Cl Dokumente und Einstellungen The UNIX programming environment htm 119 von 198 20 11 2004 11 29 42 The UNIX programming environment make clean then execution starts at the rule for clean which is normally used to remove all files except the original source code make uses some special variables which resemble the special variables used in Perl but don t confuse them The most useful one is 8 which represents the current target or the object which make would like to compile i e as make checks each file it would like to compile is set to the current filename Se This evaluates to the current target i e tne name of the object you are currently trying to build It is normal to use this as the final name of the program when compiling 2 This is used only outside of suffix rules and means the name of all the files which must be compiled in order to build the current target target filel o file2 o TAB cc o 0 T This is only used in s
159. nte und Einstellungen The UNIX programming environment htm 177 von 198 20 11 2004 11 29 42 The UNIX programming environment e keys e latex e ld e OLD LIBRARY PATH e LD LIBRARY PATH e less e In e in 8 e locate s ip lp e lpg e lpstat e lz e mkdir e mkdir e more e HOTCH e netstat e nslookup e paste e PATH e pico e pine e ping e PRINTER e PRINTER e ps file Cl Dokumente und Einstellungen The UNIX programming environment htm 178 von 198 20 11 2004 11 29 42 The UNIX programming environment e rand e rcpainto e rename in perl e repeat e rlogin e rmail e rmdir rash e Screen e sed e Set e setroot e shelltool e showmount e stderr e stdin e stdout e talk e tel e telnet e TERM e tox e texinfo e textedit e touch e uname e unlink unlink e unset e users file Cl Dokumente und Einstellungen The UNIX programming environment htm 179 von 198 20 11 2004 11 29 42 The UNIX programming environment e i e vmstat e vmunix x e w e whereis e which e while e who e write e xarchie e xcalc e xdvi e xodit e xemacs e xfig e xmosaic e xpaint e xrn e xterm e xv e xxgdb e zmail e OR e logical OR Concept Index file Cl Dokumente und Einstellungen The UNIX programming environment htm
160. ocessing on the World Wide Web It has simple built in constructs for searching and replacing text storing information in arrays and retrieving them in sorted form All of the these things have previously been possible using the UNIX shell commands sed file Cl Dokumente und Einstellungen The UNIX programming environment htm 74 von 198 20 11 2004 11 29 42 The UNIX programming environment awk cut paste but these commands were designed to work primarily in the Bourne shell and are a bit awk ward to use for all but the simplest applications sed is a stream editor It takes command line instructions reads input from the stream stdin and produces output on stdout according to those instructions sed works line by line from the start of a textfile awk is a pattern matching and processing language It takes a textfile and reads it line by line matching regular expressions and acting on them awk is powerful enough to have conditional instructions like if then else and uses C s printf construction for output p Takes a line of input and cuts it into fields separated by some character For instance a normal line of text is a string of words separated by spaces Each word is a different field cut can be used for instance to pick out the third column in a table Any character can be specified as the separator paste is the logical opposite of cut It concatenates math n files and makes each line in
161. oinfo Show rpc information showmount Show clients mounting local filesystems System identity uname Display system name and operating system release hostname Show the name of this host domainname Show the name of the local NIS domain Normally this is chosen to be the same as the BIND DNS domain but it need not be nslookup Interrogate the DNS BIND name service hostname to IP address conversion Internet resources archie xarchie Search the internet ftp database for files xrn fnews Read news browser netscape xmosaic Read world wide web WWW browser Text formatting and postscript tex latex Donald Knuth s text formatting language pronounced tek the x is really a greek chi Used widely for technical publications Compiles to dvi device independent file format texinfo A hypertext documentation system using tex and info format This is the GNU documentation system This UNIX guide is written in texinfo xdvi View a tex dvi file on screen dvips Convert dvi format into postscript ghostview ghostscript View a postscript file on screen file Cl Dokumente und Einstellungen The UNIX programming environment htm 27 von 198 20 11 2004 11 29 42 The UNIX programming environment Picture editors and processors XV Handles edits and processes pictures in a variety of standard graphics formats gif jpg tiff etc Use xv quit to place a picture on your root window xpaint A simple paint pro
162. omainname e domainname command e DOS e Drawing program e du command e dvi to postscript e ed e egrep command e eim mailer e emacs e Embedded shell e Encryption e End of file CTRL D e env command e Environment variables Environment variables e Environment variables in C Environment variables in C e Environment variables in perl Environment variables in perl e Environment unix user e envpinC e eg and in perl e Error messages e Errors in perl e Executable making programs e Exiting on errors in perl e EXPORT command in sh e Exporting filesystems e Expressions regular e extern variables e Extracting filename components e fg command e File access permission file Cl Dokumente und Einstellungen The UNIX programming environment htm 186 von 198 20 11 2004 11 29 42 The UNIX programming environment e File handles in perl e File hierarchy e File mode changing e File protection bits e File transfer e File type determining in C e Filename completion e Files in perl e Files iterating over lines e Fileysystem table e find command find command e Finding commands e Finding FTP files e _finger service e fmgr file manager e fnews news reader e For loop e for loop in perl e for loop in sh e For loops in perl e foreach e foreach example e Foreach loop e foreach loop in perl e Foreground process e
163. on a CPU in Tokyo it can ask the server in Massachusetts to display its window for it e When more than one window is on a user s display it eventually becomes necessary to move the windows around and then figure out which windows are on top of which other windows etc If all of the drawing information is kept in a server it is straightforward to work out this information If every client drew where it wanted to it would be impossible to know which window was supposed to be on top of another In X the window manager is a different program to the server which does the drawing of graphics but the client server idea still applies it just has one more piece to its puzzle How to set up X windows The X windows system is large and complex and not particularly user friendly When you log in to the system X reads two files in your home directory which decide which applications will be started what they will look like The files are called Xsession This file is a shell script which starts up a number of applications as background processes and exits by calling a window manager Here is a simple example file bin csh xsession file setenv PATH usr bin bin local gnu bin usr X11R6 bin List applications here with amp at the end so they run in the background db db de xterm T NewTitle sl 1000 geometry 90x45 16 150 sb amp xclock xbiff geometry 80x80 510 0 amp Start a window manager Exec replaces
164. on t call test programs test There is a UNIX command which is already called test and chances are that when you try to run your program you will start the UNIX command instead This can cause a lot of confusion because the UNIX command doesn t seem to do very much at all What you should know before starting One library several interfaces file Cl Dokumente und Einstellungen The UNIX programming environment htm 6 von 198 20 11 2004 11 29 41 The UNIX programming environment The core of unix is the library of functions written in C which access the system Everything you do on a unix system goes through this set of functions However you can choose your own interface to these library functions Unix has very many different interfaces to its libraries in the form of languages and command interpreters You can use the functions directly in C or you can use command programs like 1s ca etc These functions just provide a simple user interface to the C calls You can also use a variety of script languages C shell Bourne shell Perl Tcl scheme You choose the interface which solves your problem most easily Unix commands are files With the exception of a few simple commands which are built into the command interpreter shell all unix commands and programs consist of executable files In other words there is a separate executable file for each command This makes it extremely simple to add new commands to the system One simpl
165. one to cut and paste between windows regardless of which host the shell runs on The components of the X window system The X11 system is based on the client server model You might wonder why a window system would be based on a model which was introduced for interprocess communication or network communication The answer is straightforward The designers of the X window system realized that network communication was to be the paradigm of the next generation of computer systems They wanted to design a system of windows which would enable a user to sit at a terminal in Massachusetts and work on a machine in Tokyo and still be able to get high quality windows displayed on their terminal The aim of X windows from the beginning is to create a distributed window environment When log onto my friend s Hewlett Packard workstation to use the text editor because don t like the one on my EUNUCHS workstation want it to work correctly on my screen with my keyboard even though my workstation is manufactured by a different company also want the colours to be right despite the fact that the HP machine uses a completely different video hardware to my machine When press the curly brace key want to see a curly brace and not some hieroglyphic because the HP station uses a different keyboard These are the problems which X tries to address In a network environment we need a common window system which will work on any kind of hardware an
166. ope disk hfs defaults 0 2 fidibus mn fidibus fys mn fidibus fys nfs rw nosuid 0 0 fidibus usr spool mail usr mail nfs rw suid 0 0 fidibus mn fidibus ul mn fidibus ul nfs fw suid 0 0O fidibus mn fidibus u2 mn fidibus u2 nfs rw suid 0 0 hassel mn hassel ul mn hassel ul nfs rw suid 0 0 The syntax of the command is mount filesystem directory type options There are two main types of filesystem a disk filesystem ufs hfs which means a physical disk and the nfs network filesystem If we mount a 4 2 filesystem it means that it is by definition a local disk on our system and is described by some logical device name like dev something If we mount an nfs filesystem we must specify the name of the filesystem and the name of the host to which the physical disk is attached Here are some examples using the SunOS filesystem list above mount a i mount all in fstab file Cl Dokumente und Einstellungen The UNIX programming environment htm 160 von 198 20 11 2004 11 29 42 The UNIX programming environment mount at nfs mount all in fstab which are type nfs mount at 4 2 mount all in fstab which are type 4 2 mount var spool mail mount only this fs with options given in fstab The t option does not work on all UNIX implementations Of course we can type the commands manually too if there is no entry in the filesystem table For example to mount an nfs filesystem on machine gandalf called site
167. or controlling several user processes 4 C shell provides some commands for starting and stopping processes These originate from the days before windows and X11 so some of them may seem a little old fashioned They are still very useful nonetheless Let s begin by looking at the commands which are true for any shell Most programs are run in the foreground or interactively That means that they are connected to the standard input and send their output to the standard output A program can be made to run in the background if it does not need to use the standard I O For example a program which generates output and sends it to a file could run in the background In a window environment programs which create their own windows can also be started as background processes leaving standard I O in the shell free Background processes run independently of what you are doing in the foreground Unix Processes and BSD signals A background process is started using the special charcter amp at the end of the command line find name lib print gt amp output amp The final amp on the end of this line means that the job will be run in the background Note that this is not confused with the redirection operator amp since it must be the last character on the line The command above looks for any files in the system containing the string lib and writes the list of files to a file called output This might be a useful way of searchi
168. ork client machines as well as to all users A straightforward Perl script or C program could implement this feature on other UNIX implementations Mount export and filesystems mount and umount To make a disk partition appear as part of the file tree it has to be mounted We say that a particular filesystem is mounted on a directory The command mount mounts filesystems and disks defined in the filesystem table file This is a file which holds data for mount to read The filesystem table has different names on different implementations of UNIX Solaris 1 SunOS etc fstab Solaris 2 etc vfstab HPUX etc checklist AIX etc filesystems IRIX etc fstab ULTRIX file Cl Dokumente und Einstellungen The UNIX programming environment htm 159 von 198 20 11 2004 11 29 42 The UNIX programming environment etc fstab OSFI etc fstab LINUX etc fstab These files also have different syntax on different machines The eventual standard which most systems comply with SunOS HPUX OSF1 is SunOS 4 Solaris 1 dev sd0a 4 2 rw Ta dev sd0g usr 4 2 rw 2 NES gluino mn gluino pc mn gluino pc nfs rw bg hard intr 0 0 fidibus var spool mail var spool mail nfs rw bg hard intr 0 0 fidibus mn fidibus ul mn fidibus ul nfs rw bg hard intr 0 0 idibus mi tidibus 12 mn fidibus u2 nfs rw bg hard intr 0 0 In HPUX HPUX dev dsk c201d6s0 hfs defaults 0 1 dev dsk c201d5s0 mn h
169. ote unix system file Cl Dokumente und Einstellungen The UNIX programming environment htm 22 von 198 20 11 2004 11 29 42 The UNIX programming environment rsh Open a shell on a remote system require access rights telnet Open a connection to a remove system using the telnet protocol Text editors ed An ancient line editor Visual interface to ed This is the only standard unix text editor supplied by vendors emacs The most powerful UNIX editor A fully configurable user programmable editor which works under X11 and on tty terminals xemacs A pretty version of emacs for X11 windows pico A tty terminal only editor comes as part of the PINE mail package xedit A test X11 only editor supplied with X windows textedit A simple X1 1 only editor supplied by Sun Microsystems File handling commands ls List files in specified directory like dir on other systems cp Copy files mv Move or rename files touch Creates an empty new file if none exists or updates date and time stamps on existing files rm unlink Remove a file or link delete mkdir rmdir Make or remove a directory A directory must be empty in order to be able to remove it cat Concatenate or join together a number of files The output is written to the standard output by default Can also be used to simply print a file on screen lp lpr Line printer Send a file to the default printer or the printer defined in the PRINTER evironment variab
170. ou should never do in UNIX Some of these will cause you more serious problems than others You can make your own list as you discover more You should NEVER EVER switch off the power on a Unix computer unless you know what you are doing A Unix machine is not like a PC running DOS Even when you are not doing anything the system is working in the background If you switch off the power you could interrupt the system while it is writing to the disk drive and destroy your disk You must also remember that several users might be using the system even though you cannot see them they do not have to be sitting at the machine they could be logged in over the network If you switch off the power you might ruin their valuable work Once you have deleted a UNIX file using rm it is impossible to recover it Don t use wildcards with rm without thinking quite carefully about what you are doing It has happened to very many users throughout the history of UNIX that one tries to type rm An but instead by a slip of the hand one writes rm Xo Unix then takes these wildcards in turn so that the first command is rm which deletes all of your files BE CAREFUL Don t ever call a program or an important file core Many scripts go around deleting files called core because the when a program crashes UNIX dumps the entire kernel image to a file called core and these files use up a lot of disk space If you call a file core it might get deleted D
171. ourish in this method is that you can also refer to the name of the program itself as 0 For example bin csh f echo This is program 0 running for Suser Sargv represents all the arguments You can also use from the Bourne shell Sub shells The C shell does not allow you to define subroutines or functions but you can create a local shell with its own private variables by enclosing commands in parentheses bin csh cd etc cd usr bin ls gt myfile file Cl Dokumente und Einstellungen The UNIX programming environment htm 50 von 198 20 11 2004 11 29 42 The UNIX programming environment pwd This program changes the working directory to etc and then executes a subshell which inside the brackets changes directory to usr bin and lists the files there The output of this private shell are sent to a file myfile At the end we print out the current working directory just to show that the cd command in brackets had no effect on the main program Normally both parentheses must be on the same line If a subshell command line gets too long so that the brackets are not on the same line you have to use backslash characters to continue the lines command command command Tests and conditions No programming language would be complete without tests and loops C shell has two kinds of decision structure the if then else andthe switch structure These are closely related to their C
172. p exit 1 parent else if wait amp status pid printf Wait for child failed n perror wait return false else if WIFSIGNALED status printf Script s returned return false if L WIFEXITED Statius return false if WEXITSTATUS status return true else return false s n comm WTERMSIG status file Cl Dokumente und Einstellungen The UNIX programming environment htm 132 von 198 20 11 2004 11 29 42 The UNIX programming environment OR KKK k k HH X k HH HK HH HH ck ck ck ck ck kc kc k ck ckck ck ckckckck ck kk k SplitCommand comm arg char comm arg maxshellargs bufsize char sp ine dom 03 char buff bufsize for sp comm sp NULL sptt bzero buff bufsize if i gt maxshellargs 1 yyerror Too many arguments in embedded script FatalError Use a wrapper while sp sp Nt sptt switch sp case TAI escanf sp buff break case sscanf sp buff break default sscanf sp s buff break for jJ 0 j lt bufsize J arg i j buff j sp strlen arg i ld return 1 file Cl Dokumente und Einstellungen The UNIX programming environment htm 133 von 198 20 11 2004 11 29 42 The UNIX programming environment In this example the script waits fo
173. pen logfile n open ps bin ps aux die Couldn t open a pipe from ps n skip first line ps max process ps close ps file Cl Dokumente und Einstellungen The UNIX programming environment htm 90 von 198 20 11 2004 11 29 42 The UNIX programming environment print logfile max process close logfile sleep 60 Sa Shy Dg Sd Se Sf Sg Ssize stat Slogfile if size gt 500 print STDERR Log file getting big better quit n exit 0 Example reading databases Here is an example program with several of the above features demonstrated simultaneously This following program lists all users who have home directories on the current host If the home area has sub directories corresponding to groups then this is specified on the command line The word home causes the program to print out the home directories of the users local bin perl HEHEHE EH EEE EH EE EH EE EE EH HE HE EE HH HEE HH HE EEE HH EEE EE HH ES 2 2 EH allusers list all users on named host i e all users who can log into this machine Syntax allusers group allusers mygroup home allusers myhost group home the current host It will not find users which cannot be validated in the passwd file or in the named groups in NIS It assumes that the users belonging to different groups are saved in subdirectories of home hostname NOTE This command returns only users who are r
174. perl while lt gt Print Here we have made heavy use of the many default assumptions which perl makes The program is simple but difficult to understand for novices First of all we use the default file handle lt gt which means take one line of input from a default file This object returns true as long as it has not reached the end of the file so this loop continues to read lines until it reaches the end of file The default file is standard input unless this script is invoked with a command line argument in which case the argument is treated as a filename and perl attempts to open the argument filename for reading The print statement has no argument telling it what to print but perl takes this to mean print the default variable _ We can therefore write this more explicitly as follows local bin perl open HANDLE SARGV 1 while lt HANDLE gt print Here we have simply filled in the assumptions explicitly The command HANDLE now reads a single line from the named file handle into the default variable _ To make this program more general we can elimiate the defaults entirely local bin perl open HANDLE SARGV 1 while Sline lt HANDLE gt print line zz and eq file Cl Dokumente und Einstellungen The UNIX programming environment htm 86 von 198 20 11 2004 11 29 42 The UNIX programming environment Be careful to distinguish between the comparison oper
175. privileged user in UNIX All other users have only restricted access to the system Usually this is desirable but sometimes it is a nuisance A setuid script is a script which has its setuid bit set When such a script is executed by a user it is run with all the rights and privileges of the owner of the script All of the commands in the script are executed as the owner of the file and not with the user id of the person who ran the script If the owner of the setuid script is root then the commands in the script are run with root privileges Setuid scripts are clearly a touchy security issue When giving away one s rights to another user especially those of root one is tempting hackers Setuid scripts should be avoided A setgid program is almost the same but only the group id is set to that of the owner of the file Often the effect is the same An example of a setuid program is the ps program ps lists all of the processes running in the kernel In order to do this it needs permission to access the private data structures in the kernel By making ps setgid root it allows ordinary users to be able to read as much as the writers of ps thought fit but no more Naturally only the superuser can make a file setuid or setgid root Summary Limitations of shell programming To summarize the last two long and oppressive chapters we shall take a step back from the details and look at what we have achieved The idea behind
176. process shell commands from C This sounds complicated but it is necessary because of the way unix handles processes If we had no use for the return value we could simply execute a shell command using the system shell command function which does all this for us but when system exits we can only tell if the command was executed successfully or unsuccessfully we learn nothing about what actually failed the shell or command which was executed under the shell If we require detailed information about what happened to the child process then we need to do the following include lt sys types h gt finclude lt sys wait h gt Send complete command as a string including all arguments ShellCommandReturnsZero comm char comm int status i argc pid pid C C har arg maxshellargs bufsize har argv Build argument array for execv call for i 0 1 lt maxshellargs i bzero arg i bufsize argc SplitCommand comm arg if pid fork lt 0 FatalError Failed to fork new process else if pid 0 child file Cl Dokumente und Einstellungen The UNIX programming environment htm 131 von 198 20 11 2004 11 29 42 The UNIX programming environment argv malloc arge l1 sizeot char Lor 1 ea s large use argv i rg i argv i char NULL if execv arg 0 argv 1 yyerror script failed perror execv
177. r I study at a href http www iu hioslo no H amp oslash gskolen i Oslo lt a gt BODY lt HTML gt ENDMARKER Other supported functions Perl has very many functions which come directly from the C library To give a taster a few are listed here The Perl book contains a comprehensive description of these Fork The standard UNIX fork command for spawning new processes Sockets Support for network socket communication Directories Directory opening and handling routines Databases Reading from the password files and the host databases is supported through the standard C functions getpasswdbyname etc dressed up to look like Perl Crypt The password encryption function Regexp Regular expressions and pattern matching search and replace functions as in sed Operators Perl has the full set of C s logical operators File testing Tests from the shell like if f file Here are some of the most frequently used functions chmod Change the file mode of a file e g chmod 755 filename chdir Change the current working directory e g chdir etc stat Get info about permissions ownership and type of a file file Cl Dokumente und Einstellungen The UNIX programming environment htm 100 von 198 20 11 2004 11 29 42 The UNIX programming environment open Open a file for reading writing as a pipe close Close an open file handle system Execute a shell command as a child process
178. r be a complete and self contained work Certain topics are covered in more detail than others Some topics are included for future reference and are not intended to be part of an introductory course but will probably be useful later The chapter on X11 programming has been deleted for the time being Comments to Mark Burgess iu hioslo no Oslo June 1996 Welcome If you are coming to unix for the first time from a Windows or Macintosh environment be prepared for a rather different culture than the one you are used to Unix is not about products and off the shelf software it is about open standards free software and the ability to change just about everything e What you personally might perceive as user friendliness in other systems others might file Cl Dokumente und Einstellungen The UNIX programming environment htm 1 von 198 20 11 2004 11 29 41 The UNIX programming environment perceive as annoying time wasting Unix offers you just about every level of friendliness and unfriendliness if you choose your programs right In this book we take the programmer s point of view e Unix is about functionality not about simplicity Be prepared for powerful not necessarily simple solutions You should approach Unix the way you should approach any new system with an open mind The journey begins Overview In this manual the word host is used to refer to a single computer system i e a single machine which has a name
179. r spool mail Change dir foreach uid echo Suid has mail in the intray space prevents an error end The sequence bin csh means that the following commands are to be fed into bin file Cl Dokumente und Einstellungen The UNIX programming environment htm 49 von 198 20 11 2004 11 29 42 The UNIX programming environment csh The two symbols must be the very first two characters in the file The option means that your cshrc file is not read by the shell when it starts up The file containing this script must be executable see chmod and must be in the current path like all other programs Like C programs C shell scripts can accept command line arguments Suppose you want to make a program to say hello to some other users who are logged onto the system Say hello mark sarah mel To do this you need to know the names that were typed on the command line These names are copied into an array in the C shell called the argument vector or argv To read these arguments you just treat argv as an array bin csh f Di Say hello foreach name Sargv echo Saying hello to Sname echo Hello from Suser write Sname end The elements of the array can be referred to as argv 1 argv argv as usual They can also be referred to as 1 3 upto the last acceptable number This makes C shell compatible with the Bourne shell as far as arguments are concerned One extra fl
180. r the exit signal from the child process before continuing The return value from the child is available from the wait function with the help of a set of macros defined in usr include sys wait h The value is given by WTERMSIG status In the final example we can open a pipe to a process directly in a C program as though it were a file by using the function popen Pipes may be opened for reading or for writing in exactly the same way as a file is opened The child process is automatically synchronized with the parent using this method Here is a program which opens a unix command for reading both stdout and stderr from the child process are piped into the program Notice that the syntax used in this call is that used by the Bourne shell since this is build deeply into the unix execution design define bufsize 1024 FILE pp char VBUFF bufsize if pp popen sbin mount va 2 amp 1 r NULL printf Failed to open pipe n return errorcode while feof pp fgets VBUFF bufsize pp Just write the output to stdout printf Pipe read 5Xn VBUFFE pclose pp Traps and signals Processes can receive signals from the UNIX kernel at any time Some of these signals terminate the execution of the program This can cause problems if the program is in the middle of critical activity such as writing to a file For that reason we can trap signals and provide our own routine for handling the
181. ram option will cause the shell to attempt to execute myprogam option filename where filename is the name of the file If a script is to accept arguments then these can be referred to as 1 2 3 9 Thereisa logical limit of nine arguments to a script but in practice it is possibile to get around this limitation 0 is the name of the script itself Here is a simple script in the Bourne shell which prints out all its arguments bin sh Print all arguments version 1 for arg in do echo Argument Sarg done echo Total number of arguments was Sf The symbol stands for the entire list of arguments like argv in C shell and is the total number of arguments like argv in C shell Another way of achieving the same is to use the shi t command We shall meet this again in the Perl programming language shift takes the first argument from the argument list and deletes it moving all of the other arguments down one number this is how we can handle long lists of arguments in sh file Cl Dokumente und Einstellungen The UNIX programming environment htm 64 von 198 20 11 2004 11 29 42 The UNIX programming environment bin sh Print all arguments version 2 while true do arg 1 shift echo Sarg was an argument if S eq 0 then break fi done Return codes All programs which execute in UNIX return a value through the C return command There i
182. rays are slightly different since they do not use numerical keys Instead they use a set of strings like in a database so that you can use one string to look up another In order to iterate over the values in the array we need to get a list of these strings The keys command is used for this Sassoc mark cool Sassoc GNU brave Sassoc zebra stripy foreach Svar keys assoc i print Svar Sassoc Svar Xn The order of the keys is not defined in the above example but you can choose to sort them alphabetically by writing foreach var sort keys assoc instead Iterating over lines in a file Since Perl is about file handling we are very interested in reading files Unlike C and C perl likes to read files line by line The angle brackets are used for this See section Files in perl Assuming that we have some file handle lt file gt for instance STDIN we can always read the file line by line with a while loop like this file Cl Dokumente und Einstellungen The UNIX programming environment htm 83 von 198 20 11 2004 11 29 42 The UNIX programming environment while Sline lt file gt print line Note that 1ine includes the end of line character on the end of each line If you want to remove it you should add a chop command while Sline lt file gt chop line print line line n Files in perl Opening files is straightforward in Perl File
183. rcury e mesg e Messages e Mime types in W3 e mkdir e mkdir command e more command e mosaic file Cl Dokumente und Einstellungen The UNIX programming environment htm 190 von 198 20 11 2004 11 29 42 The UNIX programming environment e Mounted file systems e Mounting filesystems e Moving a job to the background e Moving files e Multiple C files compiling e Multiple screens e mv command e nc e ncftp program e netstat network statistics e Network databases e Network information service e Never do in unix e NES and C support e NIS e nobody e noclobber overwrite protection e noclobber variable e nslookup command nslookup command e open command in perl e opendir command e Opening a pipe in C e Operating system name e Operators in csh e Output to file e Output sending to a file e Painting program e Panic button e Parameters in perl functions e Parser e Partitions e Parts of a filename e passwd file e paste file Cl Dokumente und Einstellungen The UNIX programming environment htm 191 von 198 20 11 2004 11 29 42 The UNIX programming environment e Paste as a perl script e paste command e PATH e path e path e Pattern matching in perl Pattern matching in perl e Pattern replacement in perl e PC windows e Perl e perl e Perl variables and types e Perl strings and scalar e Perl truncating strings e Permiss
184. re encountered in a string the shell tries to execute the command inside the quotes and replace the quoted expression by the result of that command For example unix echo This system s kernel type is This system s kernel type is vmunix unix E c c foreach file bin file vmunix sparc executable not stripped ls etc rc echo I found a config file file echo Its type is end LO S To S X und a con ig ig ype is etc rc und a con ype is etc rc boot bin file Stile ile etc re executable shell script ile etc rc boot executable shell script found a config file etc rc ip s type is etc rc ip executable shell script found a config file etc rc local s type is etc rc local ascii text found a config file etc rc local s type is etc rc local ascii text found a config file etc rc single S type is etc rc single executable shell script found a config file etc rc t executable shell script GF ct ct ct HHHHHHHHHH OW OW Wa Wa ts type is etc rc This is how we insert the result of a shell command into a text string or variable UNIX command overview Important keys CTRL A Jump to start of line If screen is active this prefixes all control key commands for screen and then the normal CTRL A is replaced by CTRL a a C
185. rn false else sprintf buffer Invalid protocol return true In the example we use streams to implement a typical input output behaviour for C A stream interface is a so called reliable protocol There are other kinds of sockets too called unrealiable or UDP sockets Features to notice on the server are that we must bind to a specific address The client is always implicitly bound to an address since a socket connection always originates from the machine on which the client is running On the server however we want to know which addresses we shall be receiving requests from In the above example we use the generic wildcard address INADDR ANY which means that any host can connect to the server Had we been more specific we could have limited communication to two machines only By calling Listen we set up a queue for incoming connections Rather than forking a separate process to handle each request we set up a queue of a certain depth If we exceed this depth then new clients rtying to connect will be refused connection The accept call is the mechanism which extracts a reply handle from the socket Using the handle obtained from this call we can reply to the client without having to open a special socket explicitly NIS The Network Information Service The network information service is a local area network database service for sharing information common to all hosts Each database is called a map The maps cont
186. rogram in sh to search for files in the current directory which contain a certain string e g search for all files which contain the word if Hint use the find command 7 Use the manual pages to find out about the commands at batch and atq Test these commands by executing the shell command date at some time of your choice Use the m option so that the result of the job is mailed to you 8 Write a script in sh or csh to list all of the files bigger than a certain size starting from the current directory and including all subdirectories This kind of program is useful for system administrators when a disk becomes full N e Perl So far we have been looking at shell programming for performing fairly simple tasks Now let s extend the idea of shell programming to cover more complex tasks like systems programming and network communications Perl is a language which was designed to retain the immediateness of shell languages but at the same time capture some of the flexibility of C Perl is an acronym for Practical extraction and report language In this chapter we shall not aim to teach Perl from scratch the best way to learn it is to use it Rather we shall concentrate on demonstrating some principles Sed and awk cut and paste One of the reasons for using Perl is that it is extremely good at textfile handling one of the most important things for UNIX users and particularly useful in connection with CGI script pr
187. rograms like 1s Solaris 1 If a non executable file is marked with the sticky bit it will not be held in the disk page cache that is it is never copied from the disk and held in RAM but is written to directly This is used to prevent certain files from using up valuable memory On some systems e g ULTRIX only the superuser can set the sticky bit On others e g SunOS any user can create a sticky directory C shell The C shell is the command interpreter which you use to run programs and utilities It contains a simple programming language for writing tailor made commands and allows you to join together unix commands with pipes It is a configurable environment and once you know it well it is the most efficient way of working with unix cshrc and login files Most users run the C shell bin csh as their login environment or these days preferably the tcsh which is an improved version of csh When a user logs in to a UNIX system the C shell starts by reading some files which configure the environment by defining variables like path e The file cshrc is searched for in your home directory i e cshrc If itis found its contents are interpreted by the C shell as C shell instructions before giving you the command prompt 3 e f and only if this is the login shell not a sub shell that you have started after login then the file login is searched for and executed With the advent of the X11 windowing sys
188. s a convention that a return value of zero 0 means that everything went well whereas any other value implies that some error occurred The return value is usually the value returned in errno the extenal error variable in C Shell scripts can test for these values either by placing the command directly inside an if test or by testing the variable which is always set to the return code of the last command Some examples are given following the next two sections Tests and conditionals The Bourne shell has the usual array of tests They are written as follows Notice that test is itself not a part of the shell but is a program which works out conditions and provides a return code See the manual page on test for more details test f file True if the file is a plain file test d file True if the file is a directory test r file True if the file is readable test w file True if the file is writable test x file True if the file is executable test s file True if the file contains something test g file True if setgid bit is set file Cl Dokumente und Einstellungen The UNIX programming environment htm 65 von 198 20 11 2004 11 29 42 The UNIX programming environment test u file True if setuid bit is set test sl s2 True if strings s1 and s2 are equal test sl s2 True if strings s1 and s2 are unequal test x eq y True if the integers x and y are numerically equal test x ne y True if integers are
189. s must be opened and closed using wait for it the commands open and close You should be careful to close files after you have finished with them especially if you are writing to a file Files are buffered and often large parts of a file are not actually written until the close command is received Three files are of course always open for every program namely STDIN STDOUT and STDERR Formally to open a file we must obtain a file descriptor or file handle This is done using open open file descrip Filename The angular brackets are used to read from the file For example line file descrip reads one line from the file associated with ile descrip Let s look at some examples of filing opening Here is how we can implement UNIX s cut and paste commands in perl local bin perl Cut in perl Cut second column while lt gt file Cl Dokumente und Einstellungen The UNIX programming environment htm 84 von 198 20 11 2004 11 29 42 The UNIX programming environment cut_array split print Hout array l yu This is the simplest way to open a file The empty file descriptor tells perl to take the argument of the command as a filename and open that file for reading This is really short for while _ lt STDIN gt with the standard input redirected to the named file The paste program can be written as follows local
190. s prance a ftopen Tile w prantt fprintf stderr popen commandi r fopen filet tar printis popen command2 w Loops and tests PEE ORE Shell foreach end if then else endif while end switch case breaksw endsw repeat i Bourne shell while do done if then else fi until do done case in esac file Cl Dokumente und Einstellungen The UNIX programming environment htm 167 von 198 20 11 2004 11 29 42 The UNIX programming environment for in do done Perl while if then else for unless else foreach until do while do until a Ud while if then else do while switch case Tor Arguments from command line C shell sargv S argv Bourne Shell Gly 2 3 St Perl SARGV S ARGV PEG ORA char argv int argc Arithmetic C shell a b c Bourne shell a expr b Se file Cl Dokumente und Einstellungen The UNIX programming environment htm 168 von 198 20 11 2004 11 29 42 The UNIX programming environment Perl a b Sc ame Om E a b t c Numerical comparison C shell if x endif Sy then Bourne shell at Sx 89 3 Jy then fi Perl if x y jo O TA if x y String comparison C shell LE oC 5S endif y then Bourne shell if x y then fi Perl if x eq y then file Cl Dokumente und Einstellungen The UNIX programming environment htm 169 von 198 20
191. s the name of the local domain and the next three lines declare the names of nameservers which will answer requests Each part of the network might have its own nameserver so as to spread the load somewhat We have to decide a primary server and two backup servers for each machine we configure This is also a natural task for a script or cfengine Network interface configuration ifconfig Perhaps even before the nameserver can be used we need to configure the network interface for our system so that it can talk to its surroundings To do this we need to set the IP address the netmask and the broadcast address for our host This job needs to be done in the startup files mentioned at the beginning of this chapter The command to set file Cl Dokumente und Einstellungen The UNIX programming environment htm 164 von 198 20 11 2004 11 29 42 The UNIX programming environment these numbers is probably in one of these scripts etc rc local ona BSD system but the manufacturer of the machine doesn t know the details of your network so you have to fill in the details yourself The command to do this is ifconfig interface configuration Here is the command to configure the author s host ifconfig le0 128 39 89 10 netmask 255 255 255 0 broadcast 128 39 89 255 This sets the IP address of the interface 1e0 to 128 39 89 10 and the netmask and broadcast addresses as indicated Although this can be done once and for all there may be mach
192. s which are searched by the shell If we had left out the break command we might have discovered that UNIX often has several programs with the same name in different directories For example bin mail usr ucb mail bin Mail bin make usr local bin make file Cl Dokumente und Einstellungen The UNIX programming environment htm 16 von 198 20 11 2004 11 29 42 The UNIX programming environment Also different versions of unix have different conventions for placing the commands in directories so the path list needs to be different for different types of unix machine In the C shell a few basic commands like cd and ki11 are built into the shell as in DOS You can find out which directory a command is stored in using the which command For example nexus which cd cd shell built in command nexus which cp bin cp nexus which only searches the directories in path and quits after the first match so if there are several commands with the same name you will only see the first of them using which Finally in the C shell the which command is built in In the Bourne shell it is a program nexus which which which shell built in command nexus sh which which usr ucb which exit nexus Take a look at the script usr ucb which It is a script written in the C shell Environment and shell variables Environment variables are variables which the shell keeps They are normally used to configure the beha
193. script language with tests and loops so that users can combine system programs to create new programs of their own e Change and remember the location of the current working directory or location within the file hierarchy The shell does not contain any more specific functions all other commands such as programs which list files or create directories etc are executable programs which are independent of the shell When you type 1s the shell looks for the executable file called 1s in a special list of directories called the command path and attempts to start this program This allows such programs to be developed and replaced independently of the actual command interpreter Each shell which is started can be customized and configured by editing a setup file For the C shell and its variants this file is called cshrc and for the Bourne shell and its variants it is called profile Note that files which begin with leading dots are not normally visible with the 1ls command Use 1s a to view these Any commands which are placed in these files are interpreted by the shell before the first command prompt is issued These files are typically used to define a command search path and terminal characteristics On each new command line you can use the cursor keys to edit the line The up arrow browses back through earlier commands CTRL a takes you to the start of the line CTRL e takes you to the end of the line The TAB can be u
194. sed to save typing with the completion facility See section file Cl Dokumente und Einstellungen The UNIX programming environment htm 15 von 198 20 11 2004 11 29 41 The UNIX programming environment Command filename completion Shell commands generally Shell commands are commands like cp mv passwd cat more less cc grep ps etc Very few commands are actually built into the shell command line interpreter in the way that they are in DOS commands are mostly programs which exist as files When we type a command the shell searches for a program with the same name and tries to execute it The file must be executable or a Command not found error will result To see what actually happens when you type a command like gcc try typing in the following C shell commands directly into a C shell We shall discuss these commands soon foreach dir path for every directory in the list path Af x odir goco then if the file is executable echo Found dir gcc Print message found break break out of loop else echo Searching dir gcc endif end The output of this command is something like Searching usr lang gcc Searching usr openwin bin gcc Searching usr openwin bin xview gcc Searching physics lib framemaker bin gcc Searching physics motif bin gcc Searching physics mutils bin gcc Searching physics common scripts gcc Found physics bin gcc If you type echo path you will see the entire list of directorie
195. served port define HOST nexus iu hioslo no define bufsize 20 file Cl Dokumente und Einstellungen The UNIX programming environment htm 145 von 198 20 11 2004 11 29 42 The UNIX programming environment ORK KKK KK kk k k k HH kk eee ee eR ck ck Ck kc kc k ck kck KK ck ck ck ck Main mul OK KKK k k k kk k k Ke HH KH KK HH kk ck kk ck kk Ck kc k ck kck HK ck ck ck ck KK main argc argv int argc char argv struct sockaddr in cin struct hostenrE hp j char buffer bufsize int sd if argc 4 printf syntax client a b n exit 1 if hp gethostbyname HOST NULL file Cl Dokumente und Einstellungen The UNIX programming environment htm 146 von 198 20 11 2004 11 29 42 The UNIX programming environment perror gethostbyname exit 1 memset amp cin 0 sizeof cin Another way to zero memory cin sin_family AF_INET cin Sin addr s addr struct in_addr hp gt h_addr gt s_addr cin sin port htons PORT printf Trying to connect to s s n HOST inet ntoa cin sin addr if sd socket AF INET SOCK STREAM 0 1 perror socket exit 1 if connect sd amp cin sizeof cin 1 perror connect exit 1 file C Dokumente und Einstellungen The UNIX programming environment htm 147 von 198 20 11 2004 11 29 42 The UNIX programming environment sporintf bufrer ss s argv 1 argv 3 if s
196. ss 129 240 22 222 Name aurora uio no Address 129 240 22 224 If no argument is given nslookup is started in interactive mode from which it is possible to use commands like help ls domain name ls h domain name ls t mx domain name list commands list hosts in the named domain list OS type list mail exchangers for hosts in domain Hb b HR de file Cl Dokumente und Einstellungen The UNIX programming environment htm 154 von 198 20 11 2004 11 29 42 The UNIX programming environment gethostbynamer This is perhaps the most important function which performs name lookup gethostbyname gets its information either from files NIS or DNS Its behaviour is configured by the files mentioned above See section DNS The Domain Name Service It is used to look up the IP address of a named host including domain name if DNS is used On the configurable systems described above the full list of servers is queried until a reply is obtained The order in which the different services are queried is important here since DNS returns a fully qualified name host name plus domain name whereas NIS and the et c hosts file database return only a hostname gethostbyname returns data in the form of a pointer to a static data structure The syntax is include netdb h Struct hostent hp hp gethostbyname myhost domain country The resulting structure varies on different implementations of UNIX but the old BSD
197. t a file by typing emacs myfile emacs is one of dozens of text editors It is not the simplest or most intuitive but it is the most powerful and if you are going to spend time learning an editor it wouldn t do any harm to make it this one You could also click on emacs icon if you are relying on a window system Emacs is almost certainly the most powerful text editor that exists on any system It is not a word processor it not for formatting printed documents but it can be linked to almost any other program in order to format and print text It contains a powerful programming language and has many intelligent features We shall not go into the details of document formatting in this book but only mention that programs like troff and Tex or Latex are used for this purpose to obtain typset quality printing Text formatting is an area where Unix folks do things differently to PC folks The login environment Unix began as a timesharing mainframe system in the seventies when the only terminals available were text based teletype terminals or tty s Later the Massachusetts Institute of Technology MIT developed the X windows interface which is now a standard across UNIX platforms Because of this history the X window system works as a front end to the standard UNIX shell and interface so to understand the user environment we must first understand the file Cl Dokumente und Einstellungen The UNIX programming environment htm 14 von 198 20 11 20
198. t with the IP address UISS 112 209 325 Clearly there must be some kind of security mechanism to prevent just anybody from opening windows on someone s display X has two such mechanisms xhost This mechanism is now obsolete The xhost command is used to define a list of hosts which are allowed to open windows on the user s display It cannot destinguish between individual users i e the command xhost yourhost would allow anyone using yourhost to access the local display This mechanism is only present for backward compatibility with early versions of X windows Normally one should use the command xhost to exclude all others from accessing the display Xauthority The Xauthority mechanism has replaced the xhost scheme It provides a security file Cl Dokumente und Einstellungen The UNIX programming environment htm 31 von 198 20 11 2004 11 29 42 The UNIX programming environment mechanism which can distinguish individual users not just hosts In order for a user to open a window on a display he she must have a ticket called a magic cookie This is a binary file called Xauthority which is created in the user s home directory when he she first starts the X windows system Anyone who does not have a recent copy of this file cannot open windows or read the display of the user s terminal This mechanism is based on the idea that the user s home directory is available via NFS on all hosts he she will log onto and thus the owner of t
199. tem this has changed slightly Since the window system takes over the entire login procedure users never get to run login shells since the login shell is file Cl Dokumente und Einstellungen The UNIX programming environment htm 37 von 198 20 11 2004 11 29 42 The UNIX programming environment used up by the X11 system On an X terminal or host running X the 1ogin file normally has no effect With some thought the 1ogin file can be eliminated entirely and we can put everything into the cshrc file Here is a very simple example cshrc file cshrc read in by every csh that starts Set the default file creation mask umask 077 Set the path set path usr local bin usr bin X11 usr ucb bin usr bin Exit here if the shell is not interactive if prompt exit Set some variables set noclobber notify filec nobeep set history 100 set prompt hostname 5 set prompt2 Sm 3h gt tcsh prompt for foreach and while setenv PRINTER myprinter setenv LD_LIBRARY_PATH usr lib usr local lib usr openwin lib Aliases are shortcuts to unix commands alias passwd yppasswd alias dir ls lg more alias sys ps aux more alias h history It is possible to make a much more complicated cshrc file than this The advent of distributed computing and NFS Network file system means that you might log into many different machines running different versions of unix The com
200. ten enough to stop any process from running Programs can choose to ignore certain signals by trapping signals with a special handler One signal they cannot ignore is signal 9 kab L27 is a sure way of killing PID 127 Even though the process dies it may not be removed from the kernel s process table if it has a parent see next section Here is the complete list of unix signals which the kernel send to processes in different circumstances 1 SIGHUP hangup 2 SIGINT interrupt 3 POTUIT quit 4 SIGILL illegal instruction not reset when caught 5 SIGTRAP trace trap not reset when caught 6 SIGIOT SIGABRT IOT instruction 7 SIGEMT EMT instruction 8 SIGFPE floating point exception 9 SIGKILL kill cannot be caught or ignored 10 SIGBUS bus error 11 SIGSEGV segmentation violation 12 SIGSYS bad argument to system call 13 SIGPIPE write on a pipe with no one to read it 14 SIGALRM alarm clock 15 SIGTERM software termination signal from kill 16 SIGURG urgent condition on IO channel 17 SIGSTOP sendable stop signal not from tty 18 SIGTSTP stop signal from tty file Cl Dokumente und Einstellungen The UNIX programming environment htm 46 von 198 20 11 2004 11 29 42 The UNIX programming environment 19 SIGCONT continue a stopped process 20
201. termed its hostname What is unix Unix is one of the most important operating system in use today perhaps even the most important Since its invention around the beginning of the 1970s it has been an object of continual research and development UNIX is not popular because it is the best operating system one could imagine but because it is an extremely flexible system which is easy to extend and modify It is an ideal platform for developing new ideas Much of the success of UNIX may be attributed to the rapid pace of its development a development to which all of its users have been able to contribute its efficiency at running programs and the many powerful tools which have been written for it over the years such as the C programming language make shell 1ex and yacc and many others UNIX was written by programmers for programmers It is popular in situations where a lot of computing power is required and for database applications where timesharing is critical In contrast to some operating systems UNIX performs equally well on large scale computers with many processors and small computers which fit in your suitcase All of the basic mechanisms required of a multi user operating system are present in UNIX During the last few years it has become ever more popular and has formed the basis of newer though less mature systems like NT One reason for this that now computers have now become powerful enough to run UNIX effectively UNIX pla
202. the data are sent in Usually a CGI script replies in HTML code in which case the first line in the reply must be Content type text html This must be followed by a blank line HTML coding of forms To start a CGI program from a web page we use a form which is a part of the HTML code enclosed with the parentheses lt FORM method POST ACTION cgi script alias program pl gt lt FORM gt The method post means that the data which get typed into this form will be piped into the CGI program via its standard input The action specifies which program you want to start Note that you cannot simply use the absolute path of the file for security reasons You must use something called a script alias to tell the web browser where to find the program If you do not have a script alias defined for you personally then you need to get one from your system administrator By using a script alias no one from outside your site can see where your files are located only that you have a cgi bin area somewhere on your system Within these parentheses you can arrange to collect different kinds of input The simplest kind of input is just a button which starts the CGI program This has the form lt INPUT TYPE submit VALUE Start my program gt file Cl Dokumente und Einstellungen The UNIX programming environment htm 103 von 198 20 11 2004 11 29 42 The UNIX programming environment This code creates a button When you click on it th
203. the name varies wildly from UNIX to UNIX mnttab on HPUX for instance The file etc rmtab on an NFS server contains a list of remote mounted filesystems which are mounted by remote clients C functions exist which can read the filesystem tables and place the resulting data in C struct types Alas these struct defintions are also quite different on different systems See usr include sys mount h so the user wishing to write system independent code is confounded at the lowest level Exercises 1 Use gethostbyname to make a simple program like ns1ookup which gives the internet address of a named host 2 Modify the client server example above to make a remote Is command called r1s You should be able to use the syntax rls options hostname path to file Basic System Administration This chapter is a brief skip through guide It is not intended to be comprehensive More a more informative guide to system and network administration see the document Network and systems administration which can be viewed on line at http www iu hioslo no CentreSciTech Setting up a UNIX machine is not always just a case of opening the box and plugging it in If it is to be connected to a network it must have an IP address be configured to contact certain servers and possibly be configured as a server itself In this chapter we consider some of the practical knowledge of a UNIX system which all administrators and programmers should know
204. this script with the fvwm process so that it doesn t exist as a separate file Cl Dokumente und Einstellungen The UNIX programming environment htm 30 von 198 20 11 2004 11 29 42 The UNIX programming environment useless process exec local bin fvwm Xdefaults This file specifies all of the resources which X programs use It can be used to change the colours used by applications or font types etc The subject of X rescources is a large one and we don t have time for it here Here is a simple example which shows how you can make your over bright xterm and emacs windows less bright grey shade xterm background LightGrey Emacs background grey92 Xemacs background grey92 X displays and authority In the terminology used by X11 every client program has to contact a display in order to open a window A display is a virtual screen which is created by the X server on a particular host X can create several separate displays on a given host though most machines only have one When an X client program wants to open a window it looks in the UNIX environment variable DISPLAY for the IP address of a host which has an X server it can contact For example if we wrote setenv DISPLAY myhost 0 the client would try to contact the X server on myhost and ask for a window on display number zero the usual display If we wrote setenv DISPLAY 198 112 208 35 0 the client would try to open display zero on the X server at the hos
205. ude lt sys stat h gt define DIRNAME define bufsize 255 KKK KKK KKK k kk k HH kk KK ee kok HH ck ck k Ck Ck kc kc ee KK KK main DIR dirh struct dirent dirp struct stat statbuf char pathname bufsize char linkname bufsize if dirh opendir DIRNAME NULL perror opendir exit 1 for dirp readdir dirh dirp NULL dirp readdir dirh if stromp dirp d name 0 strcmp dirp d name 0 continue if strcmp lost found dirp gt d name 0 continue sprintf pathname s s DIRNAME dirp gt d_name if lstat pathname amp statbuf 1 see man stat file Cl Dokumente und Einstellungen The UNIX programming environment htm 128 von 198 20 11 2004 11 29 42 The UNIX programming environment perror stat continue if S ISREG statbuf st mode i printf s is a regular file n pathname if S ISDIR statbuf st mode printf s is a directory n pathname if S ISLNK statbuf st mode bzero linkname bufsize clear string readlink pathname linkname bufsize printf s is a link to s n pathname linkname printf The mode of s is o n n pathname statbuf st_mode amp 07777 closedir dirh Process control fork exec popen and system There is a number of ways in which processes can interact with one another and in which we can control their b
206. uffix rules It has the same meaning as but only in suffix rules It stands for the pre requisite or the file which must be compiled in order to make a given object Note that because make has some default rules defined in its configuration file a single file C program can be compiled very easily by typing make filename c This is equivalent to cc c filename c cc o filename filename o New suffix rules for C Standard rules for C are not often built into UNIX systems at the time of writing but we can create them in our own Makefiles very easily Here we shall use the GNU compiler g s conventions for C files Here is a sample Makefile for using C Note that the SUFFIXES command must be used to declare new endings or file extensions HEE HH HH HE EH EEE EEE EEE HH EE EE a HE EE EEE EE HH EE EE EH HH EREEREER HH This is the Makefile for g file Cl Dokumente und Einstellungen The UNIX programming environment htm 120 von 198 20 11 2004 11 29 42 The UNIX programming environment Ht it He Ht He a HEE aE HE aE HEE EAE HE AEE EAE EAE PEE EEE EEE EEE OBJ oblig3 o blocks o hardware o inode o CCPLUS g SUFFIXES C o h Program Rules filesys S OBJ S CCPLUS o filesys OBJ Extra dependencies on the header file if the header file changes we need to rebuild o oblig3 a filesys h blocks o tilesys h hardware o filesys h inode o filesys h
207. umente und Einstellungen The UNIX programming environment htm 70 von 198 20 11 2004 11 29 42 The UNIX programming environment Update the NIS database maps on a client server This program shouldn t have to be run but sometimes things go wrong and we have to force a download from the main sever PATH etc yp usr etc yp PATH MASTER myNISserver for map in auto direct auto master ethers byaddr ethers byname group bygid group byname hosts byaddr hosts byname mail aliases netgroup byhost netgroup byuser netgroup netid byname networks byaddr networks byname passwd byname passwd byuid priss byname protocols byname protocols bynumber rpc bynumber services byname services usenetgroups byname do ypxfr 1 h SMASTER Smap done Procedures and traps One of the worthy features of the Bourne shell is that it allows you to define subroutines or procedures Subroutines work just like subroutines in any other programming language They are executed in same shell not as a sub process Here is an interesting program which demonstrates two useful things at the same time First of all it shows how to make a hierachical subroutine structure using the Bourne shell Secondly it shows how the t rap directive can be used to trap signals so that Bourne shell programs can exit safely when they are killed or when CTRL C is typed bin sh How to make a signal handler in Bourne Shell using subroutines Hatt HH EE HE HH
208. utomounter is a daemon which mounts filesystems only when they are needed rather than permanently when the machine boots Both methods require a certain amount of setting up Another way of handling this problem is to use an administration tool like cfengine See section cfengine who needs a script Mount options and cross mounting The options in the filesystem table have the following meaning read write permission ro read only permission hard do not give up if the server doesn t answer do give up do not hang bg continue trying to mount in the background if server doesn t answer intr Interruptible with CTRL C suid Allow set uid programs nosuid Disallow set uid programs A deadlock situation can occur when trying to mount NFS filesystems Suppose for example that machine A mounts a filesystem from machine B Suppose also that machine B mounts its usr filesystem from machine A This is called cross mounting The usr filesystem is crucial to B indeed it cannot export any filesystems until it can execute the file usr etc rpc mountd a SunOS machine file Cl Dokumente und Einstellungen The UNIX programming environment htm 162 von 198 20 11 2004 11 29 42 The UNIX programming environment Unfortunately because the startup script etc rc local tries to mount all filesystems network and disk when A boots A waits for a response from the server on B but B is waiting for A to export its filesystems which
209. vice control ioctl The C function ioctl I O control is used to send special control commands to devices like the disk and the network interface file Cl Dokumente und Einstellungen The UNIX programming environment htm 141 von 198 20 11 2004 11 29 42 The UNIX programming environment The syntax of the function is int xo ctli fd request arg int fd request long arg The first parameter is normally as device handle or socket descriptor The second is a control parameter Lists of valid control parameters are normally defined in the system include files for a particular device They are device and system dependent so you need a local manual and som detective work to find out what they are The final parameter is a pointer to a variable which receives return data from the device ioctl commands are device specific by their nature The commands for the ethernet interface device are only partially standardized for example We could read the ethernet device which is called le0 on a Sun workstation using the following command include sys socket h Typical includes for internet include sys ioctl h include net if h include lt netinet in h gt include arpa inet h include lt netdb h gt include sys protosw h include lt net route h gt A AE db db db db dB od un trucr ifreq LER int sk struct sockaddr in sin strcpy IFR ifr name 1e0 IFR ifr ad
210. viour of utility programs like 1px which sends a file to the printer and mail which reads and sends mail so that special options do not have to be typed in every time you run these programs Any program can read these variables to find out how you have configured your working environment We shall meet these variables frequently Here are some important variables PATH The search path for shell commands sh TERM The terminal type sh and csh DISPLAY X11 the name of your display LD_LIBRARY_PATH Path to search for object and shared libraries HOST Name of this unix host PRINTER Default printer lpr file Cl Dokumente und Einstellungen The UNIX programming environment htm 17 von 198 20 11 2004 11 29 42 The UNIX programming environment HOME The path to your home directory sh path The search path for shell commands csh term The terminal type csh noclobber See below under redirection prompt The default prompt for csh home The path to your home directory csh These variables fall into two groups Traditionally the first group always have names in uppercase letters and are called environment variables whereas variables in the second group have names with lowercase letters and are called shell variables but this is only a convention The uppercase variables are global variables whereas the lower case variables are ocal variables Local variables are not defined for programs or sub shel
211. why this works for yourself Input from the user Test a user response echo Answer y n yes or no set valid false while valid false switch lt case y echo You answered yes set valid true breaksw case n echo You answered no set valid true breaksw default echo Invalid reponse try again breaksw endsw end Notice that it would have been simpler to replace the two lines set valid true breaksw by a single line break breaksw jumps out of the switch construction after which the while test fails break jumps out of the entire while loop file Cl Dokumente und Einstellungen The UNIX programming environment htm 56 von 198 20 11 2004 11 29 42 The UNIX programming environment Extracting parts of a pathname A path name consists of a number of different parts e The path to the directory where a file is held e The name of the file itself e he file extension after a dot By using one of the following modifiers we can extract these different elements h The path to the file sp The filename itself e The file extension er The complete file path minus the file extension Here are some examples and the results set f progs ctt test c echo Sf h home mark progs c echo Sf t test C echo Sf e C echo Sf r home mark progs c t test Arithmetic Before using these features in a real script we need one more possibility numerical add
212. wo example programs which show how to make a client server pair The server enters a loop and listens for connections from clients The generic address INADDR ANY is a wildcard file Cl Dokumente und Einstellungen The UNIX programming environment htm 144 von 198 20 11 2004 11 29 42 The UNIX programming environment for any address on the current local network segment as far as the nearest router The client program sends requests to the Server as a protocol in the form of a string of the type a b Normally a and b are numbers in which case the server returns their sum to the client If the message has the special form halt where the Star is arbitrary then the server shuts down Any other form of message results in an error which the server signals to the client smallexample OR KK k kk k k kk k k k ee kokok k X X X k k k k eee ee Ke ck kc ee eK KKK KK KK KK f a vy The client part of a client server pair This simply takes two rd numbers and adds them together returning the result to the client hs n Compiled with wy cc server c ry x my User types Z 3 d u a b wy halt server KK KKK KK k kk k Ke HH kk KR eee ee ck ck ck ck k ck Ck Ck kc k ck kckckckckckck ck ck ck k ck KK include lt stdio h gt include lt sys types h gt include lt sys socket h gt include lt netinet in h gt include lt netdb h gt define PORT 0x1234 Arbitrary non re
213. y like that in C or C and is used to iterate over a numerical index like this for i 0 i lt 10 i iue pa W The foreach loop The foreach loop is like its counterpart in the C shell It is used for reading elements one by one from a regular array For example foreach i array print Si Mn Iterating over elements in arrays One of the main uses for or type loops is to iterate over successive values in an array This can be done in two ways which show the essential difference between or and foreach If we want to fetch each value in an array in turn without caring about numerical indices the it is simpest to use the foreach loop Qarray split a bc def g foreach Svar array file Cl Dokumente und Einstellungen The UNIX programming environment htm 82 von 198 20 11 2004 11 29 42 The UNIX programming environment print Svar Mn This example prints each letter on a separate line If on the other hand we are interested in the index for the purposes of some calculation then the for loop is preferable Qarray split a bc def g for i 0 i lt S array i print array i n Notice that unlike the for loop idiom in C C the limit is i lt array i e less than or equal to rather than less than This is because the 4 operator does not return the number of elements in the array but rather the last element Associated ar
214. y makes a program with the desired name and places it in the appropriate directory Unix commands live in special directories usually called bin for binary files The location of these directories is recorded in a variable called path or PATH which is used by the system to search for binaries We shall return to this in more detail in later chapters Kernel and Shell Since users cannot command the kernel directly UNIX has a command language known as the shell The word shell implies a layer around the kernel A shell is a user interface or command interpreter There are two main versions of the shell plus a number of enhancements bin sh The Bourne Shell The shell is most often used for writing system scripts It is part of the original unix system bin csh The C shell This was added to unix by the Berkeley workers The commands and syntax resemble C code C shell is better suited for interactive work than the Bourne shell The program t csh is a public domain enhancement of the csh and is in common use Two improved versions of the Bourne shell also exist ksh the Korn shell and bash the Bourne again shell Although the shells are mainly tools for typing in commands which are excutable files to be loaded and run they contain features such as aliases a command history wildcard expansions and job control functions which provide a comfortable user environment The role of C file Cl Dokumente und Einstellungen The UNI
215. y of using and combining tools e learn how to make new tools and write software e learn how to understand existing software To accomplish this task we must first learn something about the shell the way in which UNIX starts programs Later we shall learn how to solve more complex problems using Perl and C Each of these is a language which can be used to put UNIX to work We must also learn when to use which tool so that we do not waste time and effort Typical uses for these different interfaces are shell Command line interaction making scripts which perform simple jobs such as running programs in batch installing new software simple system configuration and administration perl Text interpretation text formatting output filters mail robots WWW cgi common gateway interface scripts in forms password testing simple database manipulation simple client server applications Nearly all of UNIX is written in C Any program which cannot be solved quickly using shell file Cl Dokumente und Einstellungen The UNIX programming environment htm 3 von 198 20 11 2004 11 29 41 The UNIX programming environment or perl can be written in C One advantage is that C is a compiled language and many simple errors can be caught at compile time Much of UNIX s recent popularity has been a result of its networking abilities unix is the backbone of the internet No other widely available system could keep the internet alive today Once you h
216. you add a shared library to the system under Solaris and SunOS you must run the command 1dconfig making sure that the path to the library is included in LD LIBRARY PATH SunOS uses a cache file etc 1d so cache to keep current versions of libraries Knowing about important paths directory structure It is important to know how the C compiler finds the files it needs We have already mentioned the I and L options to the compilation command line In general all system include files can be found in the directory usr include and subdirectories of this directory All system libraries can be found in usr 1ib Many packages build their own libraries and keep the relevant files in separate directories so that if the system gets reinstalled they do not get deleted This is true for example of the X windows system The include and library files for this are typically kept in directories which look something like usr local X11R5 include and usr X11R6 lib Make Nowadays compilers are often sold with fancy user environments driven by menus which make it easier to compile programs Unix has similar environments but all of them use shell based command line compilation underneath the surface That is because UNIX programmers are used to writing very large programs which occupy perhaps ten or more directories and subdirectories Each directory has to be configured to the system it is being compiled upon Interactive user environm

The UNIX programming environment

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