Using git filter-branch to remove commits by their commit message

Question

Simple Version:

If I have a branch "foo-555", with a bunch of commits with messages like:

• foo 555: blah
• foo 123: blah blah
• foo 555: blah blah blah
• foo 321: blahblah

and I want to remove all the commits that don't start with "foo 555:", is there any way to do that using git filter-branch (or any other tool for that matter)?

Original Version (More Detailed):

In our repository we have a convention where every commit message starts with a certain pattern:

Redmine #555: SOME_MESSAGE

We also do a bit of rebasing to bring in the potential release branch's changes to a specific issue's branch. In other words, I might have branch "foo-555", but before I merge it in to branch "pre-release" I need to get any commits that pre-release has that foo-555 doesn't (so that foo-555 can fast-forward merge in to pre-release).

However, because pre-release sometimes changes, we sometimes wind up with situations where you bring in a commit from pre-release, but then that commit later gets removed from pre-release. It's easy to identify commits that came from pre-release, because the number from their commit message won't match the branch number; for instance, if I see "Redmine #123: ..." in my foo-555 branch, I know that its not a commit from my branch.

So now the question: I'd like to remove all of the commits that "don't belong" to a branch; in other words, any commit that:

• Is in my foo-555 branch, but not in the pre-release branch (pre-release..foo-555)
• Has a commit message that doesn't start with "Redmine #555"

but of course "555" will vary from branch to branch. Is there any way to use filter-branch (or any other tool) to accomplish this? Currently the only way I can see to do it is to do go an interactive rebase ("git rebase -i") and manually remove all the "bad" commits.

Answer 1

Here's a fast solution that uses filter-branch instead of rebasing. There's no interactivity or needing to resolve conflicts.

git filter-branch --commit-filter '
    if [ `git rev-list --all --grep "<log-pattern>" | grep -c "$GIT_COMMIT"` -gt 0 ]
    then
        skip_commit "$@";
    else
        git commit-tree "$@";
    fi'  HEAD

You'll probably want to then clean up with:

git reflog expire --expire=now
git gc --prune=now

Answer 2

Write a script to remove lines with Redmine #555:

#!/bin/sh

mv $1 $1.$$
grep -v 'Redmine #555' < $1.$$ > $1
rm -f $1.$$

Of course you can do that however you want (eg echo a script of commands to ed).

Then launch your rebase with EDITOR set to your script:

EDITOR=/path/to/script git rebase -i REVISION

Of course it still won't be guaranteed to complete -- there may be errors during the rebase caused by leaving out revisions. You can still fix them and git rebase --continue manually.