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project_management:git

git

git is a distributed version control system originally written by Linus Torvalds. The version control metadata is distributed, so every clone is a complete history of the source code. Compare this with centralized systems like SVN or CVS where, if the central repository burns down, everything is lost!

Installing git

Migrating from SVN

Install git-svn

# aptitude install git-svn

Create a temp git repo

This is where we will initially copy the SVN repository.

$ mkdir beca_lims_portal_temp
$ cd beca_lims_portal_temp

Initialize temp git repo

$ git svn init https://172.26.17.2/svn/beca_lims_portal/trunk/ --no-metadata

Map SVN users to git

Create an authors file

/home/aorth/svnauthors:

mnorling = Martin Norling <m.norling@cgiar.org>
aorth = Alan Orth <a.orth@cgiar.org>
root = Alan Orth <a.orth@cgiar.org>
akihara = Absolomon Kihara <a.kihara@cgiar.org>

Tell git about your authors

$ git config svn.authorsfile ~/svnauthors

Populate the temp git repo

$ git svn fetch

Clone from the temp repo

When doing a normal git clone it will take everything we want from the temporary repository, while leaving behind all the SVN cruft that was there to support the git-svn stuff.

$ cd ..
$ git clone beca_lims_portal_temp beca_lims_portal

See the commit history

You should see all your authors mapped from the SVN repository:

$ cd beca_lims_portal
$ git log

Tagging

Git uses two main types of tags: lightweight and annotated. A lightweight tag is very much like a branch that doesn’t change — it’s just a pointer to a specific commit. Annotated tags, however, are stored as full objects in the Git database. They’re checksummed; contain the tagger name, e-mail, and date; have a tagging message; and can be signed and verified with GNU Privacy Guard (GPG). It’s generally recommended that you create annotated tags so you can have all this information; but if you want a temporary tag or for some reason don’t want to keep the other information, lightweight tags are available too.

Without arguments, git tag creates a "lightweight" tag that is basically a branch that never moves. Normally, you want to at least pass the -a option to create an unsigned tag.

See:

Tagging the current version

git tag -a v0.2

Tagging a past version

Specify a certain commit by giving the commit's checksum (or the abbreviated checksum):

git tag -a v0.1 8e11e65

Pushing tags to origin

By default git push doesn't send tags to the remote origin; you have to tell it to do it manually.

Certain tag

$ git push origin v0.1

All tags

Push all tags which are not already on the remote origin:

$ git push origin --tags

Reverting a file to a particular revision

If you want to revert a file in the current working revision to a past revision

$git checkout <commit_hash> filename

Tips

Edit a commit

To edit a commit (like fixing a spelling or logic mistake):

  1. Look at git log and copy the first 5 or so characters from the ID of the commit you want to edit onto your clipboard.
  2. Start the interactive rebase process, pasting in the characters from the ID: git rebase –interactive ID
  3. Your editor will come up with several lines like pick d3adb33 Commit message, one line for each commit since the older one.
  4. Change the word "pick" to "edit" in front of the commit you want to change.
  5. Save and quit.
  6. Edit your project files to make the correction, then run git commit –all –amend
  7. After you’ve committed the fixed version, do git rebase –continue

Change the last commit's author

Sometimes you commit something without realizing you haven't properly configured your ~/.gitconfig. Simple amend the last commit:

$ git log -n1
commit 85f761ec52e4be90acd2dc7c9f5842e36ad7d783
Author: Alan Orth <aorth@debian.example.org>
Date:   Sun Nov 21 05:07:48 2010 -0500

    Initial Import of DSpace 1.6.2
$ git commit --amend --author 'Alan Orth <a.orth@cgiar.org>'
... vim/nano will pop up, save the commit
$ git log -n1
commit 85f761ec52e4be90acd2dc7c9f5842e36ad7d783
Author: Alan Orth <a.orth@cgiar.org>
Date:   Sun Nov 21 05:07:48 2010 -0500

    Initial Import of DSpace 1.6.2

Assume file unchanged

Certain files, like database configuration files, need to be tracked but you don't want to push changes to the remote repo. This is different than using a .gitignore file, as those files are not tracked in the repository! This allows you to have a generic database config in your repository without telling everyone your database password!

See: http://justaddwater.dk/2009/12/07/how-to-make-git-ignore-files-that-already-exist-in-your-project/

$ git update-index --assume-unchanged common/config

Assume file changed

The opposite of the above:

$ git update-index --no-assume-unchanged common/config

Configuration

~/.gitconfig

Set a default editor

The editor is used when you have to enter a commit message.

[core]
    editor = vim

Colorize git output

[color]
    ui = auto
[color "branch"]
    current = yellow reverse
    local = yellow
    remote = green
[color "diff"]
    meta = yellow bold
    frag = magenta bold
    old = red bold
    new = green bold
[color "status"]
    added = yellow
    changed = green
    untracked = cyan

Check the current git configurations

git config -l
project_management/git.txt · Last modified: 2010/11/21 13:16 by aorth