Git Class 2
Contents
1. Auto merging trash txt CONFLICT add add Merge conflict in trash txt Automatic merge failed fix conflicts and then commit the result while the file s with the conflicts will be marked up like lt lt lt lt lt lt lt HEAD My first version of trash txt My second version of trash txt gt gt gt gt gt gt gt trashi and here is where the thought comes in You must resolve this conflict by hand because git simply cannot do it So you would edit this file add it and commit it as gt git add trash txt gt git commit git remembers that you are in the middle of a merge and will set the commit message for you which of course you can edit as you please If you find yourself in the middle of a merge that you do not want to complete simply run either git merge abort or git reset hard lt lt SHA gt gt 8 Git Submodule A submodule is used for including a separate project within your git repository e g a 3rd party library Dynare Iris some project you re developing but using in multiple other projects etc It allows you to include the project within your git repository and point to a certain branch SHA whithin that project The idea is to keep the development histories of the host and submodule projects separated it is thus different than a remote pointer to a repository Further you usually do not have write access to the repository included in the submodule As a submodule is a complete git repository you2. e g shared 0640 to allow group members to read but not to write or e g shared 0644 to allow everyone to read but not to write The default is shared false which uses the default file permissions settings for the process you re using reported by umask on linux os x 2 2 From an Existing Directory and Putting it on the Server First create a git repository as detalied above gt cd myProject gt git init gt git add gt git commit m initial commit Next on the server create a bare git repo gt mkdir myProject git gt cd myProject git gt git init bare shared group Now we have an empty bare repository on the server and all the files we want to include in that repository on our computer All we need to do now is connect the two and push the changes to the repository on the server gt git remote add origin ssh user server com path to myProject git gt git push u origin master This is the regular way you would push any new branch to the repository all the u switch tells git to do is to make your local master branch track the origin master branch you just created 2 3 Bare Git Repo File Structure Is just the contents of the git directory from above in the root level Thus the bare git repo does not contain the actual composed files but rather the minimum files necessary to clone a repository and recreate the files on your local machine 3 Git Remote In git we use remotes to point to r
3. xr reword use commit but edit the commit message e edit use commit but stop for amending s squash use commit but meld into previous commit f fixup like squash but discard this commit s log message x exec run command the rest of the line using shell If you remove a line here THAT COMMIT WILL BE LOST However if you remove everything the rebase will be aborted To modify the commit history ordering commit messages etc you can then reorder the lines delete the lines and or modify the word pick according to the Commands section To accomplish what we originally wanted in this example we would change those lines to be pick fb65f2d bug fix 1 f 853c3f0 bug fix 1 update pick 7f 45c6 bug fix 2 7 Git Merge Git merge is a command that combines two or more development histories branches You can encounter it when deciding to merge some experimental branch back into the main branch as we spoke about in the first class Or you might need it if you re a gatekeeper and responsible for merging developers commits into the main git repository To merge two branches first checkout the branch you want to merge into then merge in the other branch gt git checkout master gt git merge development Easy as that Just not really If it is breathe a sigh of releif If it s not well you have some more work to do If it doesn t go well git will let you know with a message akin to
4. can view its development tree just by switching into the directory containing it So for example say you re working on GIMF or GPM and want to use the unstable versions of both Dynare and Iris Well you can simply include them as submodules to your project and update the submodule pointers as you see fit to use the bleeding edge of those two projects In Dynare we use submodules to include code developed by Sims Waggonner and Zha To create a submodule you would do the following gt git submodule add http www dynare org git frbatlanta utilities_dw git contrib ms sbvar utilities_dw This will create a directory called dynare_root contrib ms sbvar utilities_dw containing the utili ties_dw git repository The reason it points to a repository housed at dynare and not at the Atlanta Fed is that we have a cron job that runs every night replicating their repositories just for our own backup purposes Usually however a submodule will point directly to the 3rd party s git repository This creates a new file gitmodules located in the root directory with the following information submodule contrib ms sbvar utilities_dw path contrib ms sbvar utilities_dw url http www dynare org git frbatlanta utilities_dw git Now the gitmodules file and the contrib ms sbvar utilities_dw directory need to be added and committed as per usual If you don t want to point to the HEAD of the submodule you need to change into the directory a
5. git config personal located gitconfig modified using git config global and system wide varies by system modified usinggit config system These files can be edited by hand or by using the git config command Thus the commands we used last time produce the following personal git config file user name Houtan Bastani email houtan bastani ens fr color ui auto core editor emacs The ui line tells git that I want it to use color for all commands that support it e g git diff git status etc while the editor line tells it what editor I prefer for editing used by git commit git rebase i etc The Dynare project config file core repositoryformatversion 0 filemode true bare true sharedrepository 1 receive denyNonFastforwards true hooks mailinglist commit dynare org showrev git show C s echo emailprefix Dynare Git The first three lines under core are inserted when you use the bare flag when initializing a git repo Lines 4 6 were inserted because the Dynare repo was created with shared true The 6th line specifies that users cannot rewrite the git history by forcing changes into the repository As we spoke about the other day one key characteristic of git is that it stores the entire project history Thus you can always ensure this is the case with denyNonFastforwards true Of course if you want to increase the odds of shooting yourself in the foot you shoul
6. Git Class 2 Houtan Bastani t 30 August 2012 1 Creating a Git Repository For Yourself 1 1 From Nothing gt mkdir myProject gt cd myProject gt git init And that s it Now create add and commit files as usual 1 2 From an Existing Directory gt cd myProject gt git init And that s it Now you ll need to add all the files that you want to have in the repository the commit message can be something like initial commit because there s nothing to revert and commit as usual Of course there s no pushing because this repository is just for you 1 3 File Structure of Private Repo Under the root project folder change into the git directory and take a look at what s there drwxr xr x 2 houtan staff 68B Aug 30 09 30 branches SEW E r 1 houtan staff 111B Aug 30 09 30 config rw r r 1 houtan staff 73B Aug 30 09 30 description maa a a 1 houtan staff 23B Aug 30 09 30 HEAD drwxr xr x 12 houtan staff 408B Aug 30 09 30 hooks drwxr xr x 3 houtan staff 102B Aug 30 09 30 info drwxr xr x 4 houtan staff 136B Aug 30 09 30 objects drwxr xr x 4 houtan staff 136B Aug 30 09 30 refs e branches is depricated and only here for historical reasons only used by older versions of git e config lists the configuration for the git repository Can be edited by hand or by using the git config command See Section 4 e description only used with GitWeb a git web interface used for browsing repositories e HEAD The b
7. d buy a gun and thus you can set this value to false if you want to tempt fate Of course there are many other key value pairs we ll talk about those hooks below and you just have to look at the manual to see which ones will enable you to use git in the way you prefer 5 Hooks Hooks are just shell scripts that run before and or after certain git commands are executed They can be set both on the client side and on the server side Actually when you initialize a git repository by default you are provided with sample hooks Listing the contents of the hooks directory of a new git repository shows the following files applypatch msg sample post commit sample post update sample pre commit sample commit msg sample post receive sample pre applypatch sample pre rebase sample Here you have sample scripts that perform basic actions before after a certain git command is issued The names of the sample files are fairly self descriptive as to when they act and based on what action they act And the contents of these files provide a guide on which to build the actions of your dreams prepare con update samr Several useful actions are e Send an email to everyone when the main repository is updated indicating that they should now updated their local repositories e Enforce specific commit message format e Denying forced pushes can be set in config for git gt 1 6 You can use any scripting language to create a hook even Python but
8. emote repositiories Remember that git is a decentralized distributed version control system and thus every git repository is a full repository A remote simply allows us to point to other repositories Remote repositories should track the same development history as the project you re working We use remotes for fetching and pushing Thus if we have a repository on our computer that we don t share with anyone and that is completely self contained i e we won t be pulling from elsewhere then we don t need any remote repositories In such a repository if we were to run git remote v to list all remotes we would have a blank list On the other hand in a shared repository you will necessarily be fetching from a remote and if you have write access you ll be pushing too The most common remote repository is origin and for the basic git setup it s all you ll need To add a remote named origin we do gt git remote add origin ssh user server com path to myProject git using whatever protocol necessary to access the bare git repo which will set ssh user server com path to myProject gi as both the fetch and push repo for origin You won t usually need to do this because when you clone from a repository it will usually be declared as origin by default unless your system admin did something unusual At Dynare we have a layer of quality assurance between reading and writing to a repository So my local git has two rem
9. many of the actions are canned and can be found online with simple google searches Before writing your own you should probably search for one of these first 6 Git Interactive Rebase Though the idea of git is to maintain the entire development history and hence we don t want to overwrite it as we are developing we may run into situations where we want to reorder merge our commits This may happen when you are working locally and for example you have made two bug fix commits and are about to push them to the shared repo when you notice that your first bugfix commit didn t actually fix the bug You edit the code commit it but now have a tree that looks like this o master bug fix 1 update timestamp today 12 01 SHA sha3 o bug fix 2 timestamp today 12 00 SHA sha2 o bug fix 1 timestamp today 11 59 SHA shal o origin master msg timestamp whenever SHA sha0 This however breaks the defining characteristic of a commit that it reprepsents a logical change to the code because you have two commits that fix bug 1 whereas you should only have one commit that fixes bug 1 Before pushing to the shared repository we can fix this issue by using an interactive rebase command git rebase i sha0 or git rebase i origin master which will yield a screen akin to pick fb65f2d bug fix 1 pick 7 45c6 bug fix 2 pick 853c3f0 bug fix 1 update Rebase 81d5998 853c3f0 onto 81d5998 Commands p pick use commit
10. nd change the current position to the SHA that corresponds to the commit you want to use via a git reset Remember a submodule is a complete and independent git repository so you can treat it as such You can change into the submodule directory view its git commit tree modify files push fetch them and do basically whatever else you would do in a regular git repository However in your project the only thing that is ever stored is a pointer to the SHA that represents the commit you want to include in your project Finally to clone from a repository containing submodules all you need to do is the following gt git clone ssh to repository git gt cd repository gt git submodule init gt git submodule update where the penultimate line initializes the submodule and the final line brings in the entire submodule repos itory checking out the appropriate commit Whenever a submodule pointer is changed all that a user needs to do is gt git submodule update which will update the pointer to the appropraite SHA 9 Good References official http git scm com e man pages http git scm com docs e another http www kernel org pub software scm git docs v1 7 3 user manual html list of guis http git scm com downloads guis
11. otes gt git remote v origin ssh houtanb kirikou dynare org srv d_kirikou git dynare git fetch origin ssh houtanb kirikou dynare org srv d_kirikou git dynare git push personal ssh houtanb kirikou dynare org srv d_kirikou git dynare houtanb git fetch personal ssh houtanb kirikou dynare org srv d_kirikou git dynare houtanb git push Here the origin repository has the official version of Dynare while the personal repository contains a repository to which I push changes I make to be reviewed by someone else a gatekeeper before being merged into the central repository This was setup with the following command gt git remote add personal ssh houtanb kirikou dynare org srv d_kirikou git dynare houtanb git Of course I could also have used the following commands gt git remote set url push origin ssh houtanb kirikou dynare org srv d_kirikou git dynare houtanb git gt git remote v origin ssh houtanb kirikou dynare org srv d_kirikou git dynare git fetch origin ssh houtanb kirikou dynare org srv d_kirikou git dynare houtanb git push which would have the effect of fetching from the main dynare repo and pushing to my personal dynare repo without forcing me to specify a remote You should do this only if you re comfortable with it I don t do it because it adds a layer of unnecessary obfuscation 4 Git Config There are three configuration files project specific located git config modified using
12. ranch you re currently on Dynare amp GPM Teams CEPREMAP Thoutan bastani ens fr e hooks Actions to take after specified git commands are executed e g email after git commit See Section 5 e info contains an exclude file used the same way as gitignore e objects contains the contents of the database all commits e refs contains pointers to data in the objects directory Basically you don t need to know much about git plumbing Everything more or less takes care of itself However when setting up a git repo you ll probably want to change the configure file as well as add some hooks I ll talk about these in the sections specified 2 Creating a Git Repository To Share 2 1 From Nothing On The Server gt mkdir myProject git gt cd myProject git gt git init bare shared group So what do those flags mean Well the bare flag indicates that we don t want to store the actual files in this repository Remember in the non bare repo all of the necessary git files were contained in the git folder Now in the bare repository those files will be in the root folder as no one will actually be working directly from this repository People will only clone push and pull with this repo And the shared group That just tells git to set the permissions on the repository such that group members associated with it can read and write to it If you wanted a more restrictive setting you could use the typical linux octals
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