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Revision as of 06:15, 8 November 2011 by Caspar d.nomagicasia.com (Talk | contribs)

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How to create a patch

EGit can only create patches describing a single commit. This is inadequate, because it's highly

likely that you'll commit many times onto a local branch before you're ready to create a

single patch covering that series of changes.

Fortunately Git itself makes patch creation very easy. The most versatile format of its diff command is:

# git diff <commit1> <commit2> > mypatch.txt

This creates a patch 'mypatch.txt' describing the differences between commit1 and commit2.

(Remember that in Git a commit is a snapshot, not a changeset. Therefore, any two commits

can be compared.) There are other ways of using git diff, but this is the most generic way

of invoking it.

If you're creating a patch for review, then the patch should apply cleanly against origin/master.

This suggests the following workflow:

  1. Develop on a local development branch, committing as often as you like
  2. Merge origin/master into your development branch whenever you want, but at least once, right before you create your patch.
  3. Commit the merge, if it wasn't committed automatically. (Git's default behavior is to commit automatically if there are no conflicts.)
  4. Run 'git diff' as follows: git diff origin/master HEAD (assuming that your dev branch is checked out, which makes HEAD reference it)

How to apply a patch

A patch created by 'git diff' is in the unified diff format, basically the same as the output format of 'diff -c'

on a *Nix platform. Eclipse cannot apply such a patch. You'll have to use a "real" patch processor, such

as GNU patch. Most *Nix users will have this installed, or can easily obtain it from their distro's repositories.

A Windows user will have to install it from GNU's site.

Once you have GNU patch installed, navigate into the working directory of your Git repository, and invoke

the patch binary as follows:

~/my/git/repo# patch -p1 < /path/to/mypatch.txt

You can add the --dry-run switch if you want to do, well, a dry run. Inside Eclipse you'll have to refresh

your workspace to make EGit aware of the changes.