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1. For example the regular expression foo matches the string foo and no others Other regular expressions match more than one string i e the set they describe has more than one member For example the regular expression f matches the set of strings made up of any number including zero of f s As you can see some characters in regular expressions match themselves such as f and some don t such as the ones that don t match themselves instead let you specify patterns that describe many different strings To either match or search for a regular expression with the Regex library functions you must first compile it with a Regex pattern compiling function A compiled pattern is a regular expression converted to the internal format used by the library functions Once you ve compiled a pattern you can use it for matching or searching any number of times The Regex library consists of two source files regex h and regex c Regex provides three groups of functions with which you can operate on regular expressions One group the GNU group is more powerful but not completely compatible with the other two namely the POSIX and Berkeley UNIX groups its interface was designed specifically for GNU The other groups have the same interfaces as do the regular expression functions in POSIX and Berkeley UNIX We wrote this chapter with programmers in mind not users of programs such as Emacs that use Regex We
2. 3 Match within word Op erator page 20 e lt represents the match beginning of word operator see Section 4 1 4 Match beginning of word Operator page 21 e gt represents the match end of word operator see Section 4 1 5 Match end of word Op erator page 21 e w represents the match word constituent operator see Section 4 1 6 Match word constituent Operator page 21 e AW represents the match non word constituent operator see Section 4 1 7 Match non word constituent Operator page 21 e represents the match beginning of buffer operator and represents the match end of buffer operator see Section 4 2 Buffer Operators page 21 Sometimes you don t have to explicitly quote special characters to make them ordinary For instance most characters lose any special meaning inside a list see Section 3 6 List Operators page 13 In addition if the syntax bits RE_CONTEXT_INVALID_OPS and RE_CONTEXT_INDEP_OPS aren t set then for historical reasons the matcher considers special characters ordinary if they are in contexts where the operations they represent make no sense for example then the match zero or more operator represented by matches itself in the regular expression foo because there is no preceding expression on which it can operate It is poor practice however to depend on this behavior if you want a special character to be ordinary outside a li
3. Y Y ug 13 not_bol field in pattern buffer 18 num regs in struct re_regiSterS 32 open group operator and 0 0 2 0 2 eee eee 18 OF OPA iia elie elena dead eee Re pe te 13 E parenthesizing icis 16 pattern buffer initialization 004 26 pattern buffer definition of 005 24 POSIX AWG aei stocks exerc Rie DECIDIR 5 R range argument tore_search 28 te registers m ewe erp Rn 32 RE_BACKSLASH_ESCAPE_IN_LIST 005 3 RE BK PLUS GM ee Staind Sa reeda Heda OA O GA nd a 3 REA CHAR CLASSES bote de CDU PE y Yy da 3 RE_CONTEXT_INDEP_ANCHORS sees 3 RE CONTEXT INDEP ANCHORS and 18 RE_CONTEXT_INDEP_OPS 0 cece eee eee eee 3 RE_CONTEXT_INVALID_OPS 0 0 eee cece eee 3 RE DOT NEWLINE co es d diesis teas teei e 3 RE DOT NOT NULL iessis ab y em ry hae 4 RE INTERVALS csi cc a yh LEE ERE nik d 4 REZLIMITED OPS 33 isa ssa ea ee a RP Ea RU 4 RE NEWLINE ALT is sies ga edet eb E ee 4 RE NO BK BRACES 9 Y exa he ewe ed ayb 4 RE NO BK PARENS eO Abb oe POS TA plora 4 RE NO BK REFS esu ce Tee ce eem eu Tem 4 REZNO BKEVBAR iio as tr une P RI eS 4 RE NO EMPIY RANGES e bem bm e obra en 4 re nsub field set by re compile pattern 27 re_pattern_buffer definition 24 re_syntax_options initialization 26 RE_UNMATCHED_R
4. aab and group 2 the inner one matches aa Then group 1 matches ab and group 2 matches a So 1 matches ab and 2 matches a e If the group doesn t participate in a match i e it is part of an alternative not taken or a repetition operator allows zero repetitions of it then the back reference makes the whole match fail For example one O two and three 2 four 3 matches one and three and two and four but not one and four or two and three For example if the pat tern matches one and then its group 2 matches the empty string and its group 3 doesn t participate in the match So if it then matches four then when it tries to back refer ence group 3 which it will attempt to do because 3 follows the four the match will fail because group 3 didn t participate in the match You can use a back reference as an argument to a repetition operator For example a b X2 matches a followed by two or more b s Similarly a b 2 3 matches abbbb If there is no preceding digit th subexpression the regular expression is invalid Chapter 3 Common Operators 18 3 9 Anchoring Operators These operators can constrain a pattern to match only at the beginning or end of the entire string or at the beginning or end of a line 3 9 1 The Match beginning of line Operator This operator can match the empty string
5. ene FY Y YY Y du 5 2 3 Collating Elements vs Charact T8 YY cece FY eens 6 2 4 The Backslaeh Character sius wales IA xS EX Ue RES nes 7 3 Common Operators 9 2 ata e tadas 9 3 1 The Match self Operator ordinary character esses 9 3 2 The Match any character Operator VY cece Y Y uu 9 3 3 The Concatenation Operator YY YF Y FY ua 10 3 4 Repetition Operators se Dug YG GYLL x e pe ed bd 10 3 4 1 The Match zero or more Operator e 10 3 4 2 The Match one or more Operator or N Lise 11 3 4 3 The Match zero or one Operator or N Ls 11 3 4 4 Interval Operators For NM M eee 12 3 5 The Alternation Operator or M sssee YY Y Y Fun 13 3 6 List Operators and L ce ll ri S eere as 13 3 6 1 Character Class Operators 0 eee e ee 14 3 6 2 The Range Operator si ceed bere es 15 3 7 Grouping Operators or NC M eee e eee ee eee ee ees 16 3 8 The Back reference Operator digit 0c cece eee Y Ydd 17 3 9 Anchoring Operators lessen 18 3 9 1 The Match beginning of line Operator 18 3 9 2 The Match end of line Operator 0 005 18 4 GNU Operators ee eroe Re s 20 Al Word Operators es edge iw fede eis hele sed G3 uei ege 20 4 1 1 Non Emacs Syntax Tables sese 20 4 1 2 The Match word boundary Operator
6. operator represented by The character class names and their meanings are alnum letters and digits c 1 Regex therefore doesn t consider the to be the first character in the list If you put a character first in what you think is a matching list you ll turn it into a nonmatching list Chapter 3 Common Operators 15 alpha letters blank system dependent for GNU a space or tab cntrl control characters in the ASCII encoding code 0177 and codes less than 040 digit digits graph same as print except omits space lower lowercase letters print printable characters in the ASCII encoding space tilde codes 040 through 0176 punct neither control nor alphanumeric characters space space carriage return newline vertical tab and form feed upper uppercase letters xdigit hexadecimal digits 0 9 a f A F These correspond to the definitions in the C library s lt ctype h gt facility For example alpha corresponds to the standard facility isalpha Regex recognizes character class expressions only inside of lists so alpha matches any letter but alpha outside of a bracket expression and not followed by a repetition operator matches just itself 3 6 2 The Range Operator Regex recognizes range expressions inside a list They represent those characters that fall between two elements in the current collating seguence You form a range expression by putting 2 4 a range o
7. plus the character so it matches e g not e Put a range whose starting point is first in the list For example a z matches a lowercase letter or a hyphen in English in ASCII 3 7 Grouping Operators C or NC O A group also known as a subexpression consists of an open group operator any number of other operators and a close group operator Regex treats this sequence as a unit just as mathematics and programming languages treat a parenthesized expression as a unit Therefore using groups you can e delimit the argument s to an alternation operator see Section 3 5 Alternation Operator page 13 or a repetition operator see Section 3 4 Repetition Operators page 10 e keep track of the indices of the substring that matched a given group See Section 7 1 8 Using Registers page 32 for a precise explanation This lets you e use the back reference operator see Section 3 8 Back reference Operator page 17 e use registers see Section 7 1 8 Using Registers page 32 If the syntax bit RE NO BK PARENS is set then represents the open group operator and represents the close group operator otherwise and do If the syntax bit RE UNMATCHED RIGHT PAREN ORD is set and a close group operator has no matching open group operator then Regex considers it to match Chapter 3 Common Operators 17 3 8 The Back reference Op
8. represents the close interval operator This bit is relevant only if RE INTERVALS is set RE NO BK PARENS If this bit is set then C represents the open group operator and represents the close group operator if this bit isn t set then MO represents the open group operator and represents the close group operator RE NO BK REFS If this bit is set then Regex doesn t recognize V digit as the back reference operator if this bit isn t set then it does RE NO BK VBAR If this bit is set then represents the alternation operator if this bit isn t set then Al represents the alternation operator This bit is irrelevant if RE LIMITED OPS is set RE NO EMPTY RANGES If this bit is set then a regular expression with a range whose ending point collates lower than its starting point is invalid if this bit isn t set then Regex considers such a range to be empty Chapter 2 Regular Expression 5yntax 5 RE_UNMATCHED_RIGHT_PAREN_ORD If this bit is set and the regular expression has no matching open group operator then Regex considers what would otherwise be a close group operator based on how RE_NO_BK_PARENS is set to match 2 2 Predefined Syntaxes If you re programming with Regex you can set a pattern buffer s see Section 7 1 1 GNU Pat tern Buffers page 24 and Section 7 2 1 POSIX Pattern Buffers page 35 syntax field either to an arbitrary combination of synt
9. syntax you want it compiled according to by setting the variable re syntax options declared in regex h to some syntax see Chapter 2 Regular Expression Syntax page 2 To compile a regular expression use char re comp char regex regex is the address of a null terminated regular expression re_comp uses an internal pattern buffer so you can use only the most recently compiled pattern buffer This means that if you want to use a given regular expression that you ve already compiled but it isn t the latest one you ve compiled you ll have to recompile it If you call re_comp with the null string not the empty string as the argument it doesn t change the contents of the pattern buffer If re_comp successfully compiles the regular expression it returns zero If it can t compile the regular expression it returns an error string re_comp s error messages are identical to those of re_compile_pattern see Section 7 1 2 GNU Regular Expression Compiling page 26 7 3 2 BSD Searching Searching the Berkeley UNIX way means searching in a string starting at its first character and trying successive positions within it to find a match Once you ve compiled a pattern using re_comp see Section 7 3 1 BSD Regular Expression Compiling page 40 you can ask Regex to search for that pattern in a string using int re_exec char string Chapter 7 Programming with Regex 41 string is the address of the null terminated string
10. things To protect your rights we need to make restrictions that forbid anyone to deny you these rights or to ask you to surrender the rights These restrictions translate to certain responsibilities for you if you distribute copies of the software or if you modify it For example if you distribute copies of such a program whether gratis or for a fee you must give the recipients all the rights that you have You must make sure that they too receive or can get the source code And you must show them these terms so they know their rights We protect your rights with two steps 1 copyright the software and 2 offer you this license which gives you legal permission to copy distribute and or modify the software Also for each author s protection and ours we want to make certain that everyone understands that there is no warranty for this free software If the software is modified by someone else and Appendix A GNU GENERAL PUBLIC LICENSE 43 passed on we want its recipients to know that what they have is not the original so that any problems introduced by others will not reflect on the original authors reputations Finally any free program is threatened constantly by software patents We wish to avoid the danger that redistributors of a free program will individually obtain patent licenses in effect making the program proprietary To prevent this we have made it clear that any patent must be licensed for everyone s free use or n
11. 1 1 GNU Pattern Buffers page 24 and Section 7 2 1 POSIX Pattern Buffers page 35 for more information on pat tern buffers See Section 7 1 2 GNU Regular Expression Compiling page 26 Section 7 2 2 POSIX Regular Expression Compiling page 35 and Section 7 3 1 BSD Regular Expression Compiling page 40 for more information on compiling Regex considers the value of the syntax field to be a collection of bits we refer to these bits as syntax bits Im most cases they affect what characters represent what operators We describe the meanings of the operators to which we refer in Chapter 3 Common Operators page 9 Chapter 4 GNU Operators page 20 and Chapter 5 GNU Emacs Operators page 22 For reference here is the complete list of syntax bits in alphabetical order Chapter 2 Regular Expression 5yntax 3 RE BACKSLASH ESCAPE IN LISTS If this bit is set then V inside a list see Section 3 6 List Operators page 13 quotes makes ordinary if it s special the following character if this bit isn t set then is an ordinary character inside lists See Section 2 4 The Backslash Character page 7 for what V does outside of lists RE BK PLUS QM If this bit is set then represents the match one or more operator and represents the match zero or more operator if this bit isn t set then represents the match one or more operator and represents the match zero or one opera
12. CE For example a 1 is missing a close interval operator REG EBRACK For example a is missing a close list operator Chapter 7 Programming with Regex REG ERANGE For example the range ending point z that collates lower than does its starting point a in z a is invalid Also the range with the character class alpha as its starting point in alpha REG ECTYPE For example the character class name foo in foo is invalid REG EPAREN For example a is missing an open group operator and a is missing a close group operator REG ESUBREG For example the back reference 2 that refers to a nonexistent subexpression in a 2 is invalid REG EEND Returned when a regular expression causes no other more specific error REG EESCAPE For example the trailing backslash V in aV is invalid as is the one in V REG BADPAT For example in the extended regular expression syntax the empty group in aOb is invalid REG ESIZE Returned when a regular expression needs a pattern buffer larger than 65536 bytes REG ESPACE Returned when a regular expression makes Regex to run out of memory 7 2 3 POSIX Matching Matching the POSIX way means trying to match a null terminated string starting at its first character Once you ve compiled a pattern into a pattern buffer see Section 7 2 2 POSIX Regular Expression Compiling page 35
13. HRN ELA EM TERME 21 AN ees extenta dits mg fortiter a sd farther tote tu 21 A allocatedinitialization VVY 0 000 26 alternation operator 9VYV YY Y Y eee 13 alternation operator and 7 VV V Y Yu 18 AN CHONG asad y bI eee m x ee pay yddyd Nae 18 ANCHOES ioiei les bee dade UMEN RPM eM 18 AWK Y HU HU UE LUE Y Miata 5 B back reference8 VVV FFF YY o 17 Index bacltr acking s ones ettet gh gated are a OR 10 13 beginning of line operator isses 18 bracket expression 9V YY YY Y Y eee 13 buffer field set by re compile_pattern 27 buffer initialization 00000 i 26 character classes cies 14 E STOP se iss Le peru UDIN EUN Eder 5 Bimnaes expe Na dy hada d Ned cea 5 end of line 0perat0r VYY YY YY Y Y i 18 end in struct re_regiSterS 32 F fastmap initialization Y9YF lt Y o 26 fastmap accurate field set by re compile pattern TUE PER a 27 Tas voee vC p OPCION Mo tet 30 A eR ERE ORITUR y YR Y PEE YE 5 grouping iD y ddd new Beute bodie eee 16 I igTiOring CABE cdd e da 35 interval expression L Y YY YY eee eee 12 M matching list eiu RR ia ated RH eph be x 13 matching newlin 9YFF YY Y eens 13 matching with GNU functions 27 N newline anchor field in pattern buffer 18 nonmatching list Y YYY Y
14. IGHT_PAREN_ORD 44 4 REG_EXTENDED 50 cc gu aY n hr d FAR YG y er 35 REG ICASE GY pc Ea Ee v iiaa 35 REG NEWLINE 2e m hd haer Rs 36 REG NOSUB ii iced ieee RR ku YR Oo EORR 35 Tepex T DIDIT 1 regerlh ico ggg de pde e tse I edu RC anette 1 regexp Anchorinp ua deiran eR Y a Pe 18 regmatchot eu le A RARE X E RR nana 39 regs allocated VY YY eens 32 REGS FIXED na Y aie iret ea perd d ou pa ES 33 REGS_REALLOCATE aasa cece cee eee nnne 32 REGS_UNALLOCATED eese 32 regular expressions syntax of 2 Index S searching with GNU functions v 28 start argument to re search 28 start in struct re_regiSsterS 32 struct re pattern buffer definition 24 subexpressions essere 16 Syntax bliss eser URP A dete REM RI B PNEU 2 syntax field set by re compile pattern 27 syntax initialization 0 0 2 eee eee 26 syntax of regular expressions 000 2 translate initialization lesse esses 26 used field set by re_compile_pattern 27 W word boundaries matching 0000 20 Table of Contents 1 HOVER VIEW iena ree et e bet o YG CS 1 2 Regular Expression Syntax ve 2 2 1 Syntax Biss seein dew Sede wt See shal YU CE nen es 2 2 2 Predefined Syntaxes 0 cece cece
15. License or at your option any later version This program is distributed in the hope that it will be useful but WITHOUT ANY WARRANTY without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE See the GNU General Public License for more details You should have received a copy of the GNU General Public License along with this program if not write to the Free Software Foundation Inc 675 Mass Ave Cambridge MA 02139 USA Also add information on how to contact you by electronic and paper mail Ifthe program is interactive make it output a short notice like this when it starts in an interactive mode Gnomovision version 69 Copyright C 19yy name of author Gnomovision comes with ABSOLUTELY NO WARRANTY for details type show w This is free software and you are welcome to redistribute it under certain conditions type show c for details The hypothetical commands show w and show c should show the appropriate parts of the General Public License Of course the commands you use may be called something other than show w and show c they could even be mouse clicks or menu items whatever suits your program Appendix A GNU GENERAL PUBLIC LICENSE 49 You should also get your employer if you work as a programmer or your school if any to sign a copyright disclaimer for the program if necessary Here is a sample alter the names Yoyodyne Inc hereby disclaims al
16. NG WILL ANY COPYRIGHT HOLDER OR ANY OTHER PARTY WHO MAY MODIFY AND OR REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE BE LIABLE TO YOU FOR DAMAGES INCLUDING ANY GENERAL SPECIAL INCIDENTAL OR CON SEOUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE PROGRAM INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSI BILITY OF SUCH DAMAGES END OF TERMS AND CONDITIONS Appendix A GNU GENERAL PUBLIC LICENSE 48 Appendix How to Apply These Terms to Your New Programs If you develop a new program and you want it to be of the greatest possible use to the public the best way to achieve this is to make it free software which everyone can redistribute and change under these terms To do so attach the following notices to the program It is safest to attach them to the start of each source file to most effectively convey the exclusion of warranty and each file should have at least the copyright line and a pointer to where the full notice is found one line to give the program s name and a brief idea of what it does Copyright C 19yy name of author This program is free software you can redistribute it and or modify it under the terms of the GNU General Public License as published by the Free Software Foundation either version 2 of the
17. Nb 20 4 1 3 The Match within word Operator NB sssse 20 4 1 4 The Match beginning of word Operator N 21 4 1 5 The Match end of word Operator gt 0 5004 21 4 1 6 The Match word constituent Operator Nw 21 4 1 7 The Match non word constituent Operator NW 21 42 Buffer Operators necem hid Ex ate np a ae 21 4 2 1 The Match beginning of buffer Operator V5 21 4 2 2 The Match end of buffer Operator 5 21 5 GNU Emacs Operators 0 eee eee 22 5 1 Syntactic Class Operator8 VYY Y FFY FY ud 22 5 1 1 Emacs Syntax Tables VVVYYYYF eee Yu 22 5 1 2 The Match syntactic class Operator sclass 22 5 1 3 The Match not syntactic class Operator Sclass 22 6 What Gets Matched VV FF Y eee 23 7 Programming with Regex ssus 24 7 1 GNU Regex Functions 0 cece cee e 24 7 1 1 GNU Pattern Buffers 0 00 eee 24 7 1 2 GNU Regular Expression Compiling 26 T 1 37 GNU Matching uuo is a kd A dk 27 AA GNU Searchingz se ever Y ER ee aee vb vL 28 7 1 5 Matching and Searching with Split Data 29 7 1 6 Searching with Fastmaps YVVY Y FY eee eee 30 7 1 7 GNU Translate Tables YVYY YY eee Y eee 31 7 1 8 Using Register8 VYYY YY FY ud 32 7 1 9 Fre
18. Regex edition 0 12a 19 September 1992 Kathryn A Hargreaves Karl Berry Copyright c 1992 Free Software Foundation 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 Free Software Foundation instead of in the original English Chapter 1 Overview 1 1 Overview A regular expression or regexp or pattern is a text string that describes some mathematical set of strings A regexp r matches a string s if s is in the set of strings described by r Using the Regex library you can e_see if a string matches a specified pattern as a whole and e_search within a string for a substring matching a specified pattern Some regular expressions match only one string i e the set they describe has only one member
19. SIX on the other hand reguires a different interface the caller is supposed to pass in a fixed length array which the matcher fills Therefore if regs_allocated is REGS FIXED the matcher simply fills that array The following examples illustrate the information recorded in the re_registers structure In all of them O represents the open group and the close group operator The first character in the string string is at index 0 e If the regular expression has an i th group not contained within another group that matches a substring of string then the function sets regs start i to the index in string where the substring matched by the i th group begins and regs end i to the index just beyond that substring s end The function sets regs gt start 0 and regs gt end 0 to analogous information about the entire pattern For example when you match a b against ab you get 0 in regs gt start 0 and 2 in regs gt end 0 0 in regs start 1 and 2 in regs end 1 0 in regs gt start 2 and 1 in regs gt end 2 1 in regs gt start 3 and 2 in regs gt end 3 e Ifa group matches more than once as it might if followed by e g a repetition operator then the function reports the information about what the group last matched For example when you match the pattern a against the string aa you get 0 in regs gt start 0 and 2 in regs gt end 0 1in regs gt start 1 and 2 in regs gt e
20. Section 3 6 List Operators page 13 matches a newline e match beginning of line operator see Section 3 9 1 Match beginning of line Op erator page 18 matches the empty string immediately after a newline regardless of how REG NOTBOL is set see Section 7 2 3 POSIX Matching page 37 for an explanation of REG NOTBOL e match end of line operator see Section 3 9 1 Match beginning of line Operator page 18 matches the empty string immediately before a newline regardless of how REG NOTEOL is set see Section 7 2 3 POSIX Matching page 37 for an explanation of REG NOTEOL If regcomp successfully compiles the regular expression it returns zero and sets pattern buffer to the compiled pattern Except for syntax which it sets as explained above it also sets the same fields the same way as does the GNU compiling function see Section 7 1 2 GNU Regular Expression Compiling page 26 If regcomp can t compile the regular expression it returns one of the error codes listed here Except when noted differently the syntax of in all examples below is basic regular expression syntax REG BADRPT For example the consecutive repetition operators in a are invalid As an other example if the syntax is extended regular expression syntax then the repetition operator with nothing on which to operate in is invalid REG BADBR For example the count 1 in a 1 is invalid REG EBRA
21. age 22 for what happens when Regex is compiled with the preprocessor symbol emacs defined 4 1 2 The Match word boundary Operator Nb This operator represented by b matches the empty string at either the beginning or the end of a word For example brat b matches the separate word rat 4 1 3 The Match within word Operator NB This operator represented by B matches the empty string within a word For example c Brat Be matches crate but dirty Brat doesn t match dirty rat Chapter 4 GNU Operators 21 4 1 4 The Match beginning of word Operator lt This operator represented by lt matches the empty string at the beginning of a word 4 1 5 The Match end of word Operator gt This operator represented by gt matches the empty string at the end of a word 4 1 6 The Match word constituent Operator Ww This operator represented by w matches any word constituent character 4 1 7 The Match non word constituent Operator NW This operator represented by W matches any character that is not word constituent 4 2 Buffer Operators Following are operators which work on buffers In Emacs a buffer is naturally an Emacs buffer For other programs Regex considers the entire string to be matched as the buffer 4 2 1 The Match beginning of buffer Operator V This operator represented by matches the empty string at the begi
22. ar of the regular expression against the final r of the string So it backtracks discarding the match of the last a in the string It can then match the remaining ar 3 4 2 The Match one or more Operator or If the syntax bit RE LIMITED OPS is set then Regex doesn t recognize this operator Otherwise if the syntax bit RE BK PLUS QM isn t set then represents this operator if it is then does This operator is similar to the match zero or more operator except that it repeats the preceding regular expression at least once see Section 3 4 1 Match zero or more Operator page 10 for what it operates on how some syntax bits affect it and how Regex backtracks to match it For example supposing that represents the match one or more operator then ca r matches e g car and caaaar but not cr 3 4 3 The Match zero or one Operator or Y If the syntax bit RE LIMITED OPS is set then Regex doesn t recognize this operator Otherwise if the syntax bit RE BK PLUS QM isn t set then represents this operator if it is then does This operator is similar to the match zero or more operator except that it repeats the preceding regular expression once or not at all see Section 3 4 1 Match zero or more Operator page 10 to see what it operates on how some syntax bits affect it and how Regex backtracks to match it For example supposing th
23. at represents the match zero or one operator then ca r matches both car and cr but nothing else Chapter 3 Common Operators 12 3 4 4 Interval Operators or NC MY If the syntax bit RE INTERVALS is set then Regex recognizes interval expressions They repeat the smallest possible preceding regular expression a specified number of times If the syntax bit RE NO BK BRACES is set represents the open interval operator and represents the close interval operator otherwise and do Specifically supposing that and F represent the open interval and close interval operators then count matches exactly count occurrences of the preceding regular expression min matches min or more occurrences of the preceding regular expression min max matches at least min but no more than max occurrences of the preceding regular expression The interval expression but not necessarily the regular expression that contains it is invalid if e min is greater than max or e any of count min or max are outside the range zero to RE_DUP_MAX which symbol regex h defines If the interval expression is invalid and the syntax bit RE_NO_BK_BRACES is set then Regex considers all the characters in the would be interval to be ordinary If that bit isn t set then the regular expression is invalid If the interval expression is valid but there is no preceding regula
24. ax bits see Section 2 1 Syntax Bits page 2 or else to the configu rations defined by Regex These configurations define the syntaxes used by certain programs GNU Emacs POSIX Awk traditional Awk Grep Egrep in addition to syntaxes for POSIX basic and extended regular expressions The predefined syntaxes taken directly from regex h are define RE_SYNTAX_EMACS 0 define RE_SYNTAX_AWK RE_BACKSLASH_ESCAPE_IN_LISTS RE_DOT_NOT_NULL RE_NO_BK_PARENS RE_NO_BK_REFS RE_NO_BK_VBAR RE_NO_EMPTY_RANGES RE_UNMATCHED_RIGHT_PAREN_ORD define RE_SYNTAX_POSIX_AWK RE_SYNTAX_POSIX_EXTENDED RE_BACKSLASH_ESCAPE_IN_LISTS define RE_SYNTAX_GREP RE_BK_PLUS_QM RE CHAR CLASSES N RE HAT LISTS NOT NEWLINE RE INTERVALS N RE NEWLINE ALT define RE SYNTAX EGREP N RE CHAR CLASSES RE CONTEXT INDEP ANCHORS N RE CONTEXT INDEP OPS RE HAT LISTS NOT NEWLINE N RE NEWLINE ALT RE NO BK PARENS N RE NO BK VBAR define RE SYNTAX POSIX EGREP N RE SYNTAX EGREP RE INTERVALS RE NO BK BRACES P1003 2 D11 2 section 4 20 7 1 lines 5078ff define RE SYNTAX ED RE SYNTAX POSIX BASIC Chapter 2 Regular Expression 5yntax 6 define RE SYNTAX SED RE SYNTAX POSIX BASIC Syntax bits common to both basic and extended POSIX regex syntax define RE SYNTAX POSIX COMMON N RE CHAR CLASSES RE_DOT_NEWLINE RE DOT NOT NULL N RE INTERVALS RE NO EMPTY RANGES d
25. cond two or more characters can map into one collating element For example the Spanish 11 collates after 1 and before m Since POSIX s collating element preserves the essential idea of a character we use the latter more familiar term in this document Chapter 2 Regular Expression 5yntax 7 2 4 The Backslash Character The character has one of four different meanings depending on the context in which you use it and what syntax bits are set see Section 2 1 Syntax Bits page 2 It can 1 stand for itself 2 quote the next character 3 introduce an operator or 4 do nothing 1 It stands for itself inside a list see Section 3 6 List Operators page 13 if the syntax bit RE_BACKSLASH_ESCAPE_IN_LISTS is not set For example would match 2 It quotes makes ordinary if it s special the next character when you use it either e outside a list or e inside a list and the syntax bit RE BACKSLASH ESCAPE IN LISTS is set 3 It introduces an operator when followed by certain ordinary characters sometimes only when certain syntax bits are set See the cases RE BK PLUS QM RE NO BK BRACES RE NO BK VAR RE NO BK PARENS RE NO BK REF in Section 2 1 Syntax Bits page 2 Also e b represents the match word boundary operator see Section 4 1 2 Match word boundary Operator page 20 e B represents the match within word operator see Section 4 1
26. describe the Regex library in its entirety not how to write regular expressions that a particular program understands Chapter 2 Regular Expression 5yntax 2 2 Regular Expression Syntax Characters are things you can type Operators are things in a regular expression that match one or more characters You compose regular expressions from operators which in turn you specify using one or more characters Most characters represent what we call the match self operator i e they match themselves we call these characters ordinary Other characters represent either all or parts of fancier operators e g represents what we call the match any character operator which no surprise matches almost any character we call these characters special Two different things determine what characters represent what operators 1 the regular expression syntax your program has told the Regex library to recognize and 2 the context of the character in the regular expression In the following sections we describe these things in more detail 2 1 Syntax Bits In any particular syntax for regular expressions some characters are always special others are sometimes special and others are never special The particular syntax that Regex recognizes for a given regular expression depends on the value in the syntax field of the pattern buffer of that regular expression You get a pattern buffer by compiling a regular expression See Section 7
27. e sole purpose of protecting the integrity of the free software distribution system which is implemented by public license practices Many people have made generous contributions to the wide range of software distributed through that system in reliance on consistent application of that system it is up to the author donor to decide if he or she is willing to distribute software through any other system and a licensee cannot impose that choice This section is intended to make thoroughly clear what is believed to be a consequence of the rest of this License If the distribution and or use of the Program is restricted in certain countries either by patents or by copyrighted interfaces the original copyright holder who places the Program under this License may add an explicit geographical distribution limitation excluding those countries so that distribution is permitted only in or among countries not thus excluded In such case this License incorporates the limitation as if written in the body of this License The Free Software Foundation may publish revised and or new versions of the General Public License from time to time Such new versions will be similar in spirit to the present version but may differ in detail to address new problems or concerns Each version is given a distinguishing version number If the Program specifies a version number of this License which applies to it and any later version you have the option of following th
28. e terms and conditions either of that version or of any later version published by the Free Software Foundation If the Program does not specify a version number of this License you may choose any version ever published by the Free Software Foundation If you wish to incorporate parts of the Program into other free programs whose distribution conditions are different write to the author to ask for permission For software which is copyrighted by the Free Software Foundation write to the Free Software Foundation we sometimes make exceptions for this Our decision will be guided by the two goals of preserving the free status of all derivatives of our free software and of promoting the sharing and reuse of software generally NO WARRANTY BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE THERE IS NO WAR RANTY FOR THE PROGRAM TO THE EXTENT PERMITTED BY APPLICABLE LAW EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND OR OTHER PARTIES PROVIDE THE PROGRAM AS IS WITHOUT WARRANTY OF ANY KIND EITHER EXPRESSED OR IMPLIED INCLUDING BUT NOT LIMITED TO THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE THE ENTIRE RISK AS TO THE QUALITY AND PERFOR MANCE OF THE PROGRAM IS WITH YOU SHOULD THE PROGRAM PROVE DE Appendix A GNU GENERAL PUBLIC LICENSE 13 FECTIVE YOU ASSUME THE COST OF ALL NECESSARY SERVICING REPAIR OR CORRECTION IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRIT I
29. efine RE SYNTAX POSIX BASIC N RE SYNTAX POSIX COMMON RE BK PLUS QM Differs from POSIX BASIC only in that RE BK PLUS QM becomes RE LIMITED OPS i e N are not recognized Actually this isn t minimal since other operators such as aren t disabled define RE SYNTAX POSIX MINIMAL BASIC N RE SYNTAX POSIX COMMON RE LIMITED OPS define RE SYNTAX POSIX EXTENDED _RE_SYNTAX_POSIX_COMMON RE_CONTEXT_INDEP_ANCHORS RE_CONTEXT_INDEP_OPS RE_NO_BK_BRACES RE_NO_BK_PARENS RE_NO_BK_VBAR RE_UNMATCHED_RIGHT_PAREN_ORD aA A Differs from _POSIX_EXTENDED in that RE_CONTEXT_INVALID_OPS replaces RE_CONTEXT_INDEP_OPS and RE_NO_BK_REFS is added define RE SYNTAX POSIX MINIMAL EXTENDED RE SYNTAX POSIX COMMON RE CONTEXT INDEP ANCHORS RE CONTEXT INVALID OPS RE NO BK BRACES RE NO BK PARENS RE NO BK REFS RE NO BK VBAR RE UNMATCHED RIGHT PAREN ORD aA A 2 3 Collating Elements vs Characters POSIX generalizes the notion of a character to that of a collating element It defines a collating element to be a sequence of one or more bytes defined in the current collating sequence as a unit of collation This generalizes the notion of a character in two ways First a single character can map into two or more collating elements For example the German 8 collates as the collating element s followed by another collating element s Se
30. eing GNU Pattern Buffers YY YY uu 34 7 2 POSIX Regex FunctionS 9 VYY YF FF e 35 7 2 1 POSIX Pattern Buffers VYY FFY uu 35 7 2 2 POSIX Regular Expression Compiling 35 7 2 3 POSIX Matching VVVYY YY FF Y Y YY Y Yu Au 37 7 2 4 Reporting EIrrorS VV FY YY FY eee YH 38 7 2 5 Using Byte OffsetS lt YFY YF YF Y Y Y Y o 39 7 2 6 Freeing POSIX Pattern Buffers 39 7 3 BSD Regex Functions VVYY YY YY n 40 7 3 1 BSD Regular Expression Compiling 40 7 3 2 BSD Searching V lt Y YY eee FF L Y Yd 40 Appendix A GNU GENERAL PUBLIC LICENSE LES 42 Preambles rienda eee See eh oe eed oye ebrku Wu ket Ud EIFE 42 TERMS AND CONDITIONS FOR COPYING DISTRIBUTION AND MODIFICATION ici pin eee DERE 43 Appendix How to Apply These Terms to Your New Programs 48 li
31. either at the beginning of the string or after a newline character Thus it is said to anchor the pattern to the beginning of a line In the cases following represents this operator Otherwise is ordinary e It the is first in the pattern as in foo e The syntax bit RE CONTEXT INDEP ANCHORS is set and it is outside a bracket expression e It follows an open group or alternation operator as in a bM and a b See Section 3 7 Grouping Operators page 16 and Section 3 5 Alternation Operator page 13 These rules imply that some valid patterns containing cannot be matched for example foo bar if RE CONTEXT INDEP ANCHORS is set If the not bo1 field is set in the pattern buffer see Section 7 1 1 GNU Pattern Buffers page 24 then fails to match at the beginning of the string See Section 7 2 3 POSIX Matching page 37 for when you might find this useful If the newline anchor field is set in the pattern buffer then fails to match after a newline This is useful when you do not regard the string to be matched as broken into lines 3 9 2 The Match end of line Operator This operator can match the empty string either at the end of the string or before a newline character in the string Thus it is said to anchor the pattern to the end of a line It is always represented by For example foo usually matches e g foo and e g the
32. er interfaces 7 1 1 GNU Pattern Buffers To compile match or search for a given regular expression you must supply a pattern buffer A pattern buffer holds one compiled regular expression You can have several different pattern buffers simultaneously each holding a compiled pattern for a different regular expression regex h defines the pattern buffer struct as follows Space that holds the compiled pattern It is declared as unsigned char because its elements are sometimes used as array indexes unsigned char buffer Number of bytes to which buffer points unsigned long allocated Number of bytes actually used in buffer unsigned long used Syntax setting with which the pattern was compiled reg syntax t syntax Regular expressions are also referred to as patterns hence the name pattern buffer Chapter 7 Programming with Regex Pointer to a fastmap if any otherwise zero re search uses the fastmap if there is one to skip over impossible starting points for matches char fastmap Either a translate table to apply to all characters before comparing them or zero for no translation The translation is applied to a pattern when it is compiled and to a string when it is matched char translate Number of subexpressions found by the compiler size_t re_nsub Zero if this pattern cannot match the empty string one else Well in t
33. erator digit If the syntax bit RE NO BK REF isn t set then Regex recognizes back references A back reference matches a specified preceding group The back reference operator is represented by digit any where after the end of a regular expression s digit th group see Section 3 7 Grouping Operators page 16 digit must be between 1 and 9 The matcher assigns numbers 1 through 9 to the first nine groups it encounters By using one of 1 through 9 after the corresponding group s close group operator you can match a substring identical to the one that the group does Back references match according to the following in all examples below represents the open group the close group the open interval and F the close interval operator e If the group matches a substring the back reference matches an identical substring For example a M matches aa and bana na MboM matches bananabanabobana Likewise 1 matches any newline free if the syntax bit RE DOT NEWLINE isn t set string that is composed of two identical halves the matches the first half and the M1 matches the second half e Ifthe group matches more than once as it might if followed by e g a repetition operator then the back reference matches the substring the group last matched For example a b N1N2 matches aabababa first group 1 the outer one matches
34. etters to the corresponding uppercase ones Under the ASCII encoding here s how you could initialize such a table we ll call it case_fold for i O i lt 256 i case_fold i i for i Ja i lt z i case fold i i Ca A You tell Regex to use a translate table on a given pattern buffer by assigning that table s address to the translate field of that buffer If you don t want Regex to do any translation put zero into A table that maps all uppercase letters to the corresponding lowercase ones would work just as well for this purpose Chapter 7 Programming with Regex 32 this field You ll get weird results if you change the table s contents anytime between compiling the pattern buffer compiling its fastmap and matching or searching with the pattern buffer 7 1 8 Using Registers A group in a regular expression can match a posssibly empty substring of the string that regular expression as a whole matched The matcher remembers the beginning and end of the substring matched by each group To find out what they matched pass a nonzero regs argument to a GNU matching or searching function see Section 7 1 3 GNU Matching page 27 and Section 7 1 4 GNU Searching page 28 i e the address of a structure of this type as defined in regex h struct re_registers 1 unsigned num_regs regoff t start regoff t end Hh Except for possibly the num regs th element see below the ith element o
35. f the start and end arrays records information about the ith group in the pattern They re declared as C pointers but this is only because not all C compilers accept zero length arrays conceptually it is simplest to think of them as arrays The start and end arrays are allocated in various ways depending on the value of the regs allocated field in the pattern buffer passed to the matcher The simplest and perhaps most useful is to let the matcher re allocate enough space to record information for all the groups in the regular expression If regs allocated is REGS UNALLOCATED the matcher allocates 1 re_nsub another field in the pattern buffer see Section 7 1 1 GNU Pattern Buffers page 24 The extra element is set to 1 and sets regs allocated to REGS REALLOCATE Then on subsequent calls with the same pattern buffer and regs arguments the matcher reallocates more space if necessary It would perhaps be more logical to make the regs allocated field part of the re registers structure instead of part of the pattern buffer But in that case the caller would be forced to Chapter 7 Programming with Regex 33 initialize the structure before passing it Much existing code doesn t do this initialization and it s arguably better to avoid it anyway re_compile_pattern sets regs_allocated to REGS_UNALLOCATED so if you use the GNU reg ular expression functions you get this behavior by default xx document re set registers PO
36. first three characters of foo nbar Chapter 3 Common Operators 19 Its interaction with the syntax bits and pattern buffer fields is exactly the dual of s see the previous section That is beginning becomes end next becomes previous and after becomes before Chapter 4 GNU Operators 4 GNU Operators Following are operators that GNU defines and POSIX doesn t 4 1 Word Operators The operators in this section reguire Regex to recognize parts of words Regex uses a syntax table to determine whether or not a character is part of a word i e whether or not it is word constituent 4 1 1 Non Emacs Syntax Tables A syntax table is an array indexed by the characters in your character set In the ASCII encoding therefore a syntax table has 256 elements Regex always uses a char variable re syntax table as its syntax table In some cases it initializes this variable and in others it expects you to initialize it e If Regex is compiled with the preprocessor symbols emacs and SYNTAX TABLE both undefined then Regex allocates re syntax table and initializes an element i either to Sword which it defines if i is a letter number or _ or to zero if it s not e If Regex is compiled with emacs undefined but SYNTAX TABLE defined then Regex expects you to define a char variable re syntax table to be a valid syntax table e See Section 5 1 1 Emacs Syntax Tables p
37. g that couldn t start a match If you don t want re search to use a fastmap store zero in the fastmap field of the pattern buffer before calling re search Once you ve initialized a pattern buffer s fastmap field you need never do so again even if you compile a new pattern in it provided the way the field is set still reflects whether or not you want a fastmap re search will still either do nothing if fastmap is null or if it isn t compile a new fastmap for the new pattern 7 1 7 GNU Translate Tables If you set the translate field of a pattern buffer to a translate table then the GNU Regex functions to which you ve passed that pattern buffer use it to apply a simple transformation to all the regular expression and string characters at which they look A translate table is an array indexed by the characters in your character set Under the ASCH encoding therefore a translate table has 256 elements The array s elements are also characters in your character set When the Regex functions see a character c they use translate c in its place with one exception the character after a V is not translated This ensures that the operators e g B and b are always distinguishable For example a table that maps all lowercase letters to the corresponding uppercase ones would cause the matcher to ignore differences in case Such a table would map all characters except lowercase letters to themselves and lowercase l
38. he executable If distribution of executable or object code is made by offering access to copy from a designated place then offering eguivalent access to copy the source code from the same place counts as distribution of the source code even though third parties are not compelled to copy the source along with the object code 5 You may not copy modify sublicense or distribute the Program except as expressly provided under this License Any attempt otherwise to copy modify sublicense or distribute the Pro gram is void and will automatically terminate your rights under this License However parties who have received copies or rights from you under this License will not have their licenses terminated so long as such parties remain in full compliance 6 You are not reguired to accept this License since you have not signed it However nothing else grants you permission to modify or distribute the Program or its derivative works These actions are prohibited by law if you do not accept this License Therefore by modifying or distributing the Program or any work based on the Program you indicate your acceptance of this License to do so and all its terms and conditions for copying distributing or modifying the Program or works based on it 7 Each time you redistribute the Program or any work based on the Program the recipient automatically receives a license from the original licensor to copy distribute or modify the Program subjec
39. in which you want to search re_exec returns either 1 for success or 0 for failure It automatically uses a GNU fastmap see Section 7 1 6 Searching with Fastmaps page 30 Appendix A GNU GENERAL PUBLIC LICENSE 42 Appendix A GNU GENERAL PUBLIC LICENSE Version 2 June 1991 Copyright 1989 1991 Free Software Foundation Inc 675 Mass Ave Cambridge MA 02139 USA Everyone is permitted to copy and distribute verbatim copies of this license document but changing it is not allowed Preamble The licenses for most software are designed to take away your freedom to share and change it By contrast the GNU General Public License is intended to guarantee your freedom to share and change free software to make sure the software is free for all its users This General Public License applies to most of the Free Software Foundation s software and to any other program whose authors commit to using it Some other Free Software Foundation software is covered by the GNU Library General Public License instead You can apply it to your programs too When we speak of free software we are referring to freedom not price Our General Public Licenses are designed to make sure that you have the freedom to distribute copies of free software and charge for this service if you wish that you receive source code or can get it if you want it that you can change the software or use pieces of it in new free programs and that you know you can do these
40. is the string index at which you want to begin matching the first character of string is at index zero See Section 7 1 8 Using Registers page 32 for a explanation of regs you can safely pass zero Chapter 7 Programming with Regex 28 re_match matches the regular expression in pattern_buffer against the string string according to the syntax in pattern buffers s syntax field See Section 7 1 2 GNU Regular Expression Com piling page 26 for how to set it The function returns 1 if the compiled pattern does not match any part of string and 2 if an internal error happens otherwise it returns how many possibly zero characters of string the pattern matched An example suppose pattern buffer points to a pattern buffer containing the compiled pattern for ax and string points to aaaaab whereupon size should be 6 Then if start is 2 re match returns 3 i e ax would have matched the last three a s in string If start is 0 re match returns 5 i e ax would have matched all the a s in string If start is either 5 or 6 it returns zero If start is not between zero and size then re match returns 1 7 1 4 GNU Searching Searching means trying to match starting at successive positions within a string The function re search does this Before calling re search you must compile your regular expression See Section 7 1 2 GNU Regular Expression Compiling page 26 Here is the function dec
41. l copyright interest in the program Gnomovision which makes passes at compilers written by James Hacker signature of Ty Coon 1 April 1989 Ty Coon President of Vice This General Public License does not permit incorporating your program into proprietary pro grams If your program is a subroutine library you may consider it more useful to permit linking proprietary applications with the library If this is what you want to do use the GNU Library General Public License instead of this License Index Index DA M Wd LD 18 ER RE Y A GMA DYA GR FA AUR pee da 16 DS nr s UO E ETT NY oy NL QU 16 UE sls oO ED IR REUS E TA IRAE UAM PESOS E 10 elu grat sities boa clair uke ea Saute AM EL ME 13 FN a an 9 A aired y yd e eme die 14 7 QE 11 cm 13 3 qm Yegexu eic e lie ce PE RR MUI BR FA 14 He dU eui eet vs pte uu bleed yd 13 Hp p EE 13 Qum 12 n 12 bla Uon Gofyn A atte lid lative o n GY ads 11 Ou rd il du Lese bote a 13 A A Near god HE cum Nc RH NH 18 ND AD Y IH Esso YR Y Goalie FN YY YE YS FWA 7 IND colette tana Deal ale quate ence Du st COLES Na 13 NDS osa at ote Sa Gonder O nion Salas Rees ten cat Die Satan kk 21 gc dae cla 16 NO SN 16 tal ds bec teat 21 A A o ada ay a e tania 12 ladran YU WNA Y NAU EP dada AN atea ea De 13 ON ity DF EN 12 Nod n inb bte S T n d 21 e Md E E m GA En A oe 21 Dr asia 20 nue P E OD cee aeite set 20 END Maat Ii DRY GYN decine a ue qiie d 22 Pr 22 NW YH
42. laration int re search struct re pattern buffer pa tern buffer const char string const int size const int start const int range Struct re registers regs whose arguments are the same as those to re match see Section 7 1 3 GNU Matching page 27 except that the two arguments start and range replace re match s argument start If range is positive then re search attempts a match starting first at index start then at start 1 if that fails and so on up to start range if range is negative then it attempts a match starting first at index start then at start 1 if that fails and so on Chapter 7 Programming with Regex 29 If start is not between zero and size then re search returns 1 When range is positive re search adjusts range so that start range 1 is between zero and size if necessary that way it won t search outside of string Similarly when range is negative re search adjusts range so that start range 1 is between zero and size if necessary If the fastmap field of pattern buffer is zero re search matches starting at consecutive posi tions otherwise it uses fastmap to make the search more efficient See Section 7 1 6 Searching with Fastmaps page 30 If no match is found re search returns 1 If a match is found it returns the index where the match began If an internal error happens it returns 2 7 1 5 Matching and Searching with Split Data Using the functions re match 2 a
43. ly print such an announcement your work based on the Program is not reguired to print an announcement These requirements apply to the modified work as a whole If identifiable sections of that work are not derived from the Program and can be reasonably considered independent and separate works in themselves then this License and its terms do not apply to those sections when you distribute them as separate works But when you distribute the same sections as part of a whole which is a work based on the Program the distribution of the whole must be on the terms of this License whose permissions for other licensees extend to the entire whole and thus to each and every part regardless of who wrote it Thus it is not the intent of this section to claim rights or contest your rights to work written entirely by you rather the intent is to exercise the right to control the distribution of derivative or collective works based on the Program In addition mere aggregation of another work not based on the Program with the Program or with a work based on the Program on a volume of a storage or distribution medium does not bring the other work under the scope of this License 4 You may copy and distribute the Program or a work based on it under Section 2 in object code or executable form under the terms of Sections 1 and 2 above provided that you also do one of the following a Accompany it with the complete corresponding machine readable
44. nce this operator operates on the smallest preceding regular expression fo has a repeating o not a repeating fo So fox matches f fo foo and so on Since the match zero or more operator is a suffix operator it may be useless as such when no regular expression precedes it This is the case when it e_is first in a regular expression or e follows a match beginning of line open group or alternation operator Three different things can happen in these cases 1 If the syntax bit RE_CONTEXT_INVALID_OPS is set then the regular expression is invalid 2 If RE CONTEXT INVALID OPS isn t set but RE_CONTEXT_INDEP_OPS is then represents the match zero or more operator which then operates on the empty string 3 Otherwise is ordinary Chapter 3 Common Operators 11 The matcher processes a match zero or more operator by first matching as many repetitions of the smallest preceding regular expression as it can Then it continues to match the rest of the pattern If it can t match the rest of the pattern it backtracks as many times as necessary each time discarding one of the matches until it can either match the entire pattern or be certain that it cannot get a match For example when matching ca ar against caaar the matcher first matches all three a s of the string with the ax of the regular expression However it cannot then match the final
45. nd 1 e If the ith group does not participate in a successful match e g it is an alternative not taken or a repetition operator allows zero repetitions of it then the function sets regs gt start i and regs gt end i to 1 For example when you match the pattern a b against the string b you get 0 in regs gt start 0 and 1 in regs gt end 0 in regs gt start 1 and 1 in regs gt end 1 Chapter 7 Programming with Regex e If the i th group matches a zero length string then the function sets regs gt start i and regs end i to the index just beyond that zero length string For example when you match the pattern a b against the string b you get 0 in regs gt start 0 and 1 in regs gt end 0 0 in regs start 1 and 0 in regs end 1 e If an ith group contains a j th group in turn not contained within any other group within group i and the function reports a match of the i th group then it records in regs gt start j and regs end j the last match if it matched of the j th group For example when you match the pattern a b against the string abb group 2 last matches the empty string so you get what it previously matched 0 in regs gt start 0 and 3 in regs gt end 0 2 in regs gt start 1 and 3 in regs gt end 1 2 in regs gt start 2 and 2 in regs gt end 2 When you match the pattern a b against the string abb group 2 doesn t partici
46. nd re search 2 you can match or search in data that is divided into two strings The function int re match 2 struct re pattern buffer buffer const char stringl const int sizel const char string2 const int size2 const int s art struct re registers regs const int stop is similar to re match see Section 7 1 3 GNU Matching page 27 except that you pass two data strings and sizes and an index stop beyond which you don t want the matcher to try matching As with re match if it succeeds re match 2 returns how many characters of string it matched Regard stringl and string2 as concatenated when you set the arguments start and stop and use the contents of regs re match 2 never returns a value larger than sizel size2 The function int Chapter 7 Programming with Regex re search 2 struct re pattern buffer buffer const char stringl const int sizel const char string2 const int size2 const int start const int range struct re registers regs const int stop is similarly related to re search 7 1 6 Searching with Fastmaps If you re searching through a long string you should use a fastmap Without one the searcher tries to match at consecutive positions in the string Generally most of the characters in the string could not start a match It takes much longer to try matching at a given position in the string than it does to check in a table whether or not the character at that position could
47. nning of the buffer 4 2 2 The Match end of buffer Operator V This operator represented by matches the empty string at the end of the buffer Chapter 5 GNU Emacs Operators 22 5 GNU Emacs Operators Following are operators that GNU defines and POSIX doesn t that you can use only when Regex is compiled with the preprocessor symbol emacs defined 5 1 Syntactic Class Operators The operators in this section reguire Regex to recognize the syntactic classes of characters Regex uses a syntax table to determine this 5 1 1 Emacs Syntax Tables A syntax table is an array indexed by the characters in your character set In the ASCII encoding therefore a syntax table has 256 elements If Regex is compiled with the preprocessor symbol emacs defined then Regex expects you to define and initialize the variable re syntax table to be an Emacs syntax table Emacs syntax tables are more complicated than Regex s own see Section 4 1 1 Non Emacs Syntax Tables page 20 See section Syntax in The GNU Emacs User s Manual for a description of Emacs syntax tables 5 1 2 The Match syntactic class Operator Nsclass This operator matches any character whose syntactic class is represented by a specified charac ter sclass represents this operator where class is the character representing the syntactic class you want For example w represents the syntactic class of word constituent characters so sw ma
48. o this License and to the absence of any warranty and give any other recipients of the Program a copy of this License along with the Program You may charge a fee for the physical act of transferring a copy and you may at your option offer warranty protection in exchange for a fee 3 You may modify your copy or copies of the Program or any portion of it thus forming a work based on the Program and copy and distribute such modifications or work under the terms of Section 1 above provided that you also meet all of these conditions a You must cause the modified files to carry prominent notices stating that you changed the files and the date of any change Appendix A GNU GENERAL PUBLIC LICENSE b You must cause any work that you distribute or publish that in whole or in part contains or is derived from the Program or any part thereof to be licensed as a whole at no charge to all third parties under the terms of this License c If the modified program normally reads commands interactively when run you must cause it when started running for such interactive use in the most ordinary way to print or display an announcement including an appropriate copyright notice and a notice that there is no warranty or else saying that you provide a warranty and that users may redistribute the program under these conditions and telling the user how to view a copy of this License Exception if the Program itself is interactive but does not normal
49. ons declared in regex h and defined in regex c before calling the compiling function re compile pattern see below See Section 2 1 Syntax Bits page 2 and Section 2 2 Predefined Syntaxes page 5 You can change the value of re syntax options at any time Usually however you set its value once and then never change it re compile pattern takes a pattern buffer as an argument You must initialize the following fields translate initialization translate Initialize this to point to a translate table if you want one or to zero if you don t We explain translate tables in Section 7 1 7 GNU Translate Tables page 31 fastmap Initialize this to nonzero if you want a fastmap or to zero if you don t buffer allocated If you want re_compile_pattern to allocate memory for the compiled pattern set both of these to zero If you have an existing block of memory allocated with malloc you want Regex to use set buffer to its address and allocated to its size in bytes re_compile_pattern uses realloc to extend the space for the compiled pattern as necessary To compile a pattern buffer use char re_compile_pattern const char regex const int regex size struct re pattern buffer x pattern buffer Chapter 7 Programming with Regex regex is the regular expression s address regex_size is its length and pattern buffer is the pattern buffer s address If re_compile_pattern successfully compiles the regula
50. ordinary characters see Chapter 2 Regular Ex pression Syntax page 2 represent this operator For example f is always an ordinary character so the regular expression f matches only the string f In particular it does not match the string ff 3 2 The Match any character Operator This operator matches any single printing or nonprinting character except it won t match a newline if the syntax bit RE DOT NEWLINE isn t set null if the syntax bit RE DOT NOT NULL is set The period character represents this operator For example a b matches any three character string beginning with a and ending with b Chapter 3 Common Operators 10 3 3 The Concatenation Operator This operator concatenates two regular expressions a and b No character represents this op erator you simply put b after a The result is a regular expression that will match a string if a matches its first part and b matches the rest For example xy two match self operators matches e xy 3 4 Repetition Operators Repetition operators repeat the preceding regular expression a specified number of times 3 4 1 The Match zero or more Operator This operator repeats the smallest possible preceding regular expression as many times as neces sary including zero to match the pattern represents this operator For example o matches any string made up of zero or more o s Si
51. ot licensed at all The precise terms and conditions for copying distribution and modification follow TERMS AND CONDITIONS FOR COPYING DISTRIBUTION AND MODIFICATION 1 This License applies to any program or other work which contains a notice placed by the copyright holder saying it may be distributed under the terms of this General Public License The Program below refers to any such program or work and a work based on the Pro gram means either the Program or any derivative work under copyright law that is to say a work containing the Program or a portion of it either verbatim or with modifications and or translated into another language Hereinafter translation is included without limitation in the term modification Each licensee is addressed as you Activities other than copying distribution and modification are not covered by this License they are outside its scope The act of running the Program is not restricted and the output from the Program is covered only if its contents constitute a work based on the Program independent of having been made by running the Program Whether that is true depends on what the Program does 2 You may copy and distribute verbatim copies of the Program s source code as you receive it in any medium provided that you conspicuously and appropriately publish on each copy an appropriate copyright notice and disclaimer of warranty keep intact all the notices that refer t
52. pate in the last match so you get 0 in regs gt start 0 and 3 in regs gt end 0 2 in regs gt start 1 and 3 in regs gt end 1 0 in regs gt start 2 and 1 in regs gt end 2 e If an i th group contains a j th group in turn not contained within any other group within group i and the function sets regs gt start i and regs gt end i to l then it also sets regs gt start j and regs end j to 1 For example when you match the pattern a b c against the string c you get 0 in regs gt start 0 and 1 in regs gt end 0 in regs gt start 1 and 1 in regs gt end 1 in regs start 2 and 1 in regs gt end 2 7 1 9 Freeing GNU Pattern Buffers To free any allocated fields of a pattern buffer you can use the POSIX function described in Section 7 2 6 Freeing POSIX Pattern Buffers page 39 since the type regex_t the type for POSIX pattern buffers is equivalent to the type re pattern buffer After freeing a pattern buffer you need to again compile a regular expression in it see Section 7 1 2 GNU Regular Expression Compiling page 26 before passing it to a matching or searching function Chapter 7 Programming with Regex 35 7 2 POSIX Regex Functions If you re writing code that has to be POSIX compatible you ll need to use these functions Their interfaces are as specified by Posix draft 1003 2 D11 2 7 2 1 POSIX Pattern Buffers To compile or match a given regular expres
53. pattern buffer see Section 7 1 1 GNU Pattern Buffers page 24 is set then nonmatching lists do not match a newline Most characters lose any special meaning inside a list The special characters inside a list follow S ends the list if it s not the first list item So if you want to make the character a list item you must put it first Av quotes the next character if the syntax bit RE BACKSLASH ESCAPE IN LISTS is set ES represents the open character class operator see Section 3 6 1 Character Class Oper ators page 14 if the syntax bit RE CHAR CLASSES is set and what follows is a valid character class expression te represents the close character class operator if the syntax bit RE CHAR CLASSES is set and what precedes it is an open character class operator followed by a valid character class name represents the range operator see Section 3 6 2 Range Operator page 15 if it s not first or last in a list or the ending point of a range All other characters are ordinary For example matches and 3 6 1 Character Class Operators 1 If the syntax bit RE CHARACTER CLASSES is set then Regex recognizes character class expressions inside lists A character class expression matches one character from a given class You form a character class expression by putting a character class name between an open character class operator represented by and a close character class
54. perator between two characters represents the range operator For example a f within a list represents all the characters from a through f inclusively If the syntax bit RE_NO_EMPTY_RANGES is set then if the range s ending point collates less than its starting point the range and the regular expression containing it is invalid For example the regular expression z a would be invalid If this bit isn t set then Regex considers such a range to be empty Since represents the range operator if you want to make a character itself a list item you must do one of the following e Put the either first or last in the list You can t use a character class for the starting or ending point of a range since a character class is not a single character Chapter 3 Common Operators 16 e Include a range whose starting point collates strictly lower than and whose ending point collates equal or higher Unless a range is the first item in a list a can t be its starting point but can be its ending point That is because Regex considers to be the range operator unless it is preceded by another For example in the ASCII encoding 9 and are contiguous characters in the collating sequence You might think that has two ranges and Rather it has the ranges and
55. r Expression Compiling page 35 for how to set it The function returns zero if the compiled pattern matches string and REG NOMATCH defined in regex h if it doesn t 7 2 4 Reporting Errors If either regcomp or regexec fail they return a nonzero error code the possibilities for which are defined in regex h See Section 7 2 2 POSIX Regular Expression Compiling page 35 and Section 7 2 3 POSIX Matching page 37 for what these codes mean To get an error string corresponding to these codes you can use size_t regerror int errcode const regex_t preg char xerrbuf size_t errbuf size errcode is an error code preg is the address of the pattern buffer which provoked the error errbuf is the error buffer and errbuf size is errbuf s size regerror returns the size in bytes of the error string corresponding to errcode including its ter minating null If errbuf and errbuf size are nonzero it also returns in errbuf the first errbuf _size 1 characters of the error string followed by a null errbuf size must be a nonnegative number less than or egual to the size in bytes of errbuf Chapter 7 Programming with Regex 39 You can call regerror with a null errbuf and a zero errbuf size to determine how large errbuf need be to accommodate regerror s error string 7 2 5 Using Byte Offsets In POSIX variables of type regmatch t hold analogous information but are not identical to GNU s registers see Section 7 1 8 U
56. r expression it returns zero and sets pattern_buffer to the compiled pattern It sets the pattern buffer s fields as follows buffer to the compiled pattern used to the number of bytes the compiled pattern in buffer occupies syntax to the current value of re_syntax_options re nsub to the number of subexpressions in regex fastmap accurate to zero on the theory that the pattern you re compiling is different than the one pre viously compiled into buffer in that case since you can t make a fastmap without a compiled pattern fastmap would either contain an incompatible fastmap or nothing at all If re compile pattern can t compile regex it returns an error string corresponding to one of the errors listed in Section 7 2 2 POSIX Regular Expression Compiling page 35 7 1 3 GNU Matching Matching the GNU way means trying to match as much of a string as possible starting at a position within it you specify Once you ve compiled a pattern into a pattern buffer see Section 7 1 2 GNU Regular Expression Compiling page 26 you can ask the matcher to match that pattern against a string using int re match struct re pattern buffer pattern_buffer const char string const int size const int start struct re registers regs pattern buffer is the address of a pattern buffer containing a compiled pattern string is the string you want to match it can contain newline and null characters size is the length of that string start
57. r expression on which to operate then if the syntax bit RE_CONTEXT_INVALID_OPS is set the regular expression is invalid If that bit isn t set then Regex considers all the characters other than backslashes which it ignores in the would be interval to be ordinary Chapter 3 Common Operators 13 3 5 The Alternation Operator or VM If the syntax bit RE LIMITED OPS is set then Regex doesn t recognize this operator Otherwise if the syntax bit RE NO BK VBAR is set then represents this operator otherwise does Alternatives match one of a choice of regular expressions if you put the character s representing the alternation operator between any two regular expressions a and b the result matches the union 6 p of the strings that a and b match For example supposing that is the alternation operator then foo bar quux would match any of foo bar or quux The alternation operator operates on the largest possible surrounding regular expressions Put another way it has the lowest precedence of any regular expression operator Thus the only way you can delimit its arguments is to use grouping For example if C and are the open and close group operators then fo olb ar would match either fooar or fobar foolbar would match foo or bar The matcher usually tries all combinations of alternatives so as to match the longest possible st
58. ring For example when matching fooglfoo gbarguux bar against fooqbarquux it cannot take say the first depth first combination it could match since then it would be content to match just foogbar 3 6 List Operators L and 1 Lists also called bracket expressions are a set of one or more items An item is a character a character class expression or a range expression The syntax bits affect which kinds of items you can put in a list We explain the last two items in subsections below Empty lists are invalid A matching list matches a single character represented by one of the list items You form a matching list by enclosing one or more items within an open matching list operator represented by U and a close list operator represented by ad matches the empty string and any string For example ab matches either a or b composed of just a s and d s in any order Regex considers invalid a regular expression with a but no matching Chapter 3 Common Operators 14 Nonmatching lists are similar to matching lists except that they match a single character not represented by one of the list items You use an open nonmatching list operator represented by instead of an open matching list operator to start a nonmatching list For example ab matches any character except a or b If the posix_newline field in the
59. ruth it s used only in re_search_2 to see whether or not we should use the fastmap so we don t set this absolutely perfectly see re compile fastmap the duplicate case unsigned can_be_null 1 If REGS UNALLOCATED allocate space in the regs structure for max RE NREGS re_nsub 1 groups If REGS_REALLOCATE reallocate space if necessary If REGS FIXED use what s there define REGS UNALLOCATED O define REGS REALLOCATE 1 define REGS FIXED 2 unsigned regs allocated 2 Set to zero when regex compile compiles a pattern set to one by re compile fastmap if it updates the fastmap unsigned fastmap accurate 1 If set re match 2 does not return information about subexpressions unsigned no_sub 1 If set a beginning of line anchor doesn t match at the beginning of the string unsigned not_bol 1 Similarly for an end of line anchor unsigned not eol 1 If true an anchor at a newline matches unsigned newline_anchor 1 29 Chapter 7 Programming with Regex 26 7 1 2 GNU Regular Expression Compiling In GNU you can both match and search for a given regular expression To do either you must first compile it in a pattern buffer see Section 7 1 1 GNU Pattern Buffers page 24 Regular expressions match according to the syntax with which they were compiled with GNU you indicate what syntax you want by setting the variable re_syntax_opti
60. sing Registers page 32 To get information about registers in POSIX pass to regexec a nonzero pmatch of type regmatch t i e the address of a structure of this type defined in regex h typedef struct 1 regoff t rm so regoff t rm eo regmatch t When reading in Section 7 1 8 Using Registers page 32 about how the matching func tion stores the information into the registers substitute pmatch for regs pmatch il gt rm_so for regs gt start i and pmatch i rm eo for regs gt end i 7 2 6 Freeing POSIX Pattern Buffers To free any allocated fields of a pattern buffer use void regfree regex t preg preg is the pattern buffer whose allocated fields you want freed regfree also sets preg s allocated and used fields to zero After freeing a pattern buffer you need to again compile a regular expression in it see Section 7 2 2 POSIX Regular Expression Compiling page 35 before passing it to the matching function see Section 7 2 3 POSIX Matching page 37 Chapter 7 Programming with Regex 7 3 BSD Regex Functions If you re writing code that has to be Berkeley UNIX compatible you ll need to use these functions whose interfaces are the same as those in Berkeley UNIX 7 3 1 BSD Regular Expression Compiling With Berkeley UNIX you can only search for a given regular expression you can t match one To search for it you must first compile it Before you compile it you must indicate the regular expression
61. sion the POSIX way you must supply a pattern buffer exactly the way you do for GNU see Section 7 1 1 GNU Pattern Buffers page 24 POSIX pattern buffers have type regex t which is equivalent to the GNU pattern buffer type re pattern buffer 7 2 2 POSIX Regular Expression Compiling With POSIX you can only search for a given regular expression you can t match it To do this you must first compile it in a pattern buffer using regcomp To compile a pattern buffer use int regcomp regex t preg const char regex int cflags preg is the initialized pattern buffer s address regex is the regular expression s address and cflags is the compilation flags which Regex considers as a collection of bits Here are the valid bits as defined in regex h REG EXTENDED says to use POSIX Extended Regular Expression syntax if this isn t set then says to use POSIX Basic Regular Expression syntax regcomp sets preg s syntax field accordingly REG ICASE says to ignore case regcomp sets preg s translate field to a translate table which ignores case replacing anything you ve put there before REG NOSUB says to set preg s no sub field see Section 7 2 3 POSIX Matching page 37 for what this means Chapter 7 Programming with Regex 36 REG NEWLINE says that a e match any character operator see Section 3 2 Match any character Operator page 9 doesn t match a newline e nonmatching list not containing a newline see
62. source code which must be distributed under the terms of Sections 1 and 2 above on a medium customarily used for software interchange or b Accompany it with a written offer valid for at least three years to give any third party for a charge no more than your cost of physically performing source distribution a complete machine readable copy of the corresponding source code to be distributed under the terms of Sections 1 and 2 above on a medium customarily used for software interchange or c Accompany it with the information you received as to the offer to distribute corresponding source code This alternative is allowed only for noncommercial distribution and only if you received the program in object code or executable form with such an offer in accord with Subsection b above Appendix A GNU GENERAL PUBLIC LICENSE 45 The source code for a work means the preferred form of the work for making modifications to it For an executable work complete source code means all the source code for all modules it contains plus any associated interface definition files plus the scripts used to control com pilation and installation of the executable However as a special exception the source code distributed need not include anything that is normally distributed in either source or binary form with the major components compiler kernel and so on of the operating system on which the executable runs unless that component itself accompanies t
63. ssion or just after a match beginning of line open group or alternation operator or e an alternation operator first or last in the regular expression just before a match end of line operator or just after an alternation or open group operator If this bit isn t set then you can put the characters representing the repetition and alternation characters anywhere in a regular expression Whether or not they will in fact be operators in certain positions depends on other syntax bits Chapter 2 Regular Expression 5yntax 4 RE DOT NEWLINE If this bit is set then the match any character operator matches a newline if this bit isn t set then it doesn t RE DOT NOT NULL If this bit is set then the match any character operator doesn t match a null character if this bit isn t set then it does RE INTERVALS If this bit is set then Regex recognizes interval operators if this bit isn t set then it doesn t RE LIMITED OPS If this bit is set then Regex doesn t recognize the match one or more match zero or one or alternation operators if this bit isn t set then it does RE NEWLINE ALT If this bit is set then newline represents the alternation operator if this bit isn t set then newline is ordinary RE NO BK BRACES If this bit is set then represents the open interval operator and represents the close interval operator if this bit isn t set then represents the open interval operator and
64. st it s better to always guote it regardless Chapter 2 Regular Expression 5yntax 8 e If Regex was compiled with the C preprocessor symbol emacs defined then sclass repre sents the match syntactic class operator and Sclass represents the match not syntactic class operator see Section 5 1 Syntactic Class Operators page 22 4 In all other cases Regex ignores V For example n matches n Chapter 3 Common Operators 9 3 Common Operators You compose regular expressions from operators In the following sections we describe the regular expression operators specified by POSIX GNU also uses these Most operators have more than one representation as characters See Chapter 2 Regular Expression Syntax page 2 for what characters represent what operators under what circumstances For most operators that can be represented in two ways one representation is a single char b acter and the other is that character preceded by V For example either C or AC represents the open group operator Which one does depends on the setting of a syntax bit in this case RE_NO_BK_PARENS Why is this so Historical reasons dictate some of the varying representations while POSIX dictates others Finally almost all characters lose any special meaning inside a list see Section 3 6 List Oper ators page 13 3 1 The Match self Operator ordinary character This operator matches the character itself All
65. start a match A fastmap is such a table More specifically a fastmap is an array indexed by the characters in your character set Under the ASCII encoding therefore a fastmap has 256 elements If you want the searcher to use a fastmap with a given pattern buffer you must allocate the array and assign the array s address to the pattern buffer s fastmap field You either can compile the fastmap yourself or have re_search do it for you when fastmap is nonzero it automatically compiles a fastmap the first time you search using a particular compiled pattern To compile a fastmap yourself use int re_compile_fastmap struct re_pattern_buffer pattern_buffer pattern_buffer is the address of a pattern buffer If the character c could start a match for the pattern re_compile_fastmap makes pattern buffer fastmap c nonzero It returns 0 if it can compile a fastmap and 2 if there is an internal error For example if is the alternation operator and pattern buffer holds the compiled pattern for alb then re_compile_fastmap sets fastmap a and fastmap b and no others re search uses a fastmap as it moves along in the string it checks the string s characters until it finds one that s in the fastmap Then it tries matching at that character If the match fails Chapter 7 Programming with Regex 31 it repeats the process So by using a fastmap re search doesn t waste time trying to match at positions in the strin
66. t to these terms and conditions You may not impose any further restrictions on the recipients exercise of the rights granted herein You are not responsible for enforcing compliance by third parties to this License 8 If as a consequence of a court judgment or allegation of patent infringement or for any other reason not limited to patent issues conditions are imposed on you whether by court order agreement or otherwise that contradict the conditions of this License they do not excuse you from the conditions of this License If you cannot distribute so as to satisfy simultaneously your obligations under this License and any other pertinent obligations then as a conseguence you may not distribute the Program at all For example if a patent license would not permit royalty free redistribution of the Program by all those who receive copies directly or indirectly through you then the only way you could satisfy both it and this License would be to refrain entirely from distribution of the Program If any portion of this section is held invalid or unenforceable under any particular circumstance the balance of the section is intended to apply and the section as a whole is intended to apply in other circumstances Appendix A GNU GENERAL PUBLIC LICENSE 46 10 11 12 It is not the purpose of this section to induce you to infringe any patents or other property right claims or to contest validity of any such claims this section has th
67. tches any word constituent character 5 1 3 The Match not syntactic class Operator Sclass This operator is similar to the match syntactic class operator except that it matches any char acter whose syntactic class is not represented by the specified character Sclass represents this operator For example w represents the syntactic class of word constituent characters so Sw matches any character that is not word constituent Chapter 6 What Gets Matched 23 6 What Gets Matched Regex usually matches strings according to the leftmost longest rule that is it chooses the longest of the leftmost matches This does not mean that for a regular expression containing subexpressions that it simply chooses the longest match for each subexpression left to right the overall match must also be the longest possible one For example ac c d ac 1 matches acdacaaa not acdac as it would if it were to choose the longest match for the first subexpression Chapter 7 Programming with Regex 7 Programming with Regex Here we describe how you use the Regex data structures and functions in C programs Regex has three interfaces one designed for GNU one compatible with POSIX and one compatible with Berkeley UNIX 7 1 GNU Regex Functions If you re writing code that doesn t need to be compatible with either POSIX or Berkeley UNIX you can use these functions They provide more options than the oth
68. tor This bit is irrelevant if RE LIMITED OPS is set RE CHAR CLASSES If this bit is set then you can use character classes in lists if this bit isn t set then you can t RE CONTEXT INDEP ANCHORS If this bit is set then and are special anywhere outside a list if this bit isn t set then these characters are special only in certain contexts See Section 3 9 1 Match beginning of line Operator page 18 and Section 3 9 2 Match end of line Operator page 18 RE CONTEXT INDEP OPS If this bit is set then certain characters are special anywhere outside a list if this bit isn t set then those characters are special only in some contexts and are ordinary else where Specifically if this bit isn t set then and if the syntax bit RE LIMITED OPS isn t set and or and depending on the syntax bit RE BK PLUS QM represent repetition operators only if they re not first in a regular expression or just after an open group or alternation operator The same holds for or depending on the syntax bit RE NO BK BRACES if it is the beginning of a valid interval and the syntax bit RE INTERVALS is set RE CONTEXT INVALID OPS If this bit is set then repetition and alternation operators can t be in certain positions within a regular expression Specifically the regular expression is invalid if it has e arepetition operator first in the regular expre
69. you can ask the matcher to match that pattern against a string using int regexec const regex_t preg const char string size_t nmatch regmatch_t pmatch int eflags preg is the address of a pattern buffer for a compiled pattern string is the string you want to match Chapter 7 Programming with Regex 38 See Section 7 2 5 Using Byte Offsets page 39 for an explanation of pmatch If you pass zero for nmatch or you compiled preg with the compilation flag REG_NOSUB set then regexec will ignore pmatch otherwise you must allocate it to have at least nmatch elements regexec will record nmatch byte offsets in pmatch and set to 1 any unused elements up to pmatch nmatch 1 eflags specifies execution flags namely the two bits REG NOTBOL and REG NOTEOL defined in regex h If you set REG NOTBOL then the match beginning of line operator see Section 3 9 1 Match beginning of line Operator page 18 always fails to match This lets you match against pieces of a line as you would need to if say searching for repeated instances of a given pattern in a line it would work correctly for patterns both with and without match beginning of line operators REG NOTEOL works analogously for the match end of line operator see Section 3 9 2 Match end of line Operator page 18 it exists for symmetry regexec tries to find a match for preg in string according to the syntax in preg s syntax field See Section 7 2 2 POSIX Regula

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