This is a simple script which makes it easier for me to batch-rewrite the first lines of my commit messags.

$ git rmsg SHA

This will pop up your $EDITOR with the first lines of commit messages of the commits between SHA and HEAD. Edit that file, changing each commit's name to the desired name, and exit your editor. git rmsg will then rewrite history, changing the name of each of these commits to the name you provided.

Lines following the first line in each commit message will be preserved without changes.

If your commit message contains the string "Part N", it will be rewritten to contain the correct part number. For example if you write the commit messages:

Bug 100 - Part N: Cheese
Bug 100 - Part N: Pear
Bug 100 - Part N: Apple
Bug 100 - Part N: Coconut

The messages will be rewritten to:

Bug 100 - Part 4: Cheese
Bug 100 - Part 3: Pear
Bug 100 - Part 2: Apple
Bug 100 - Part 1: Coconut

The script generates a small python script which will look up, based on the commit message passed over stdin, the commit message you wrote. It will then pass this script as an msg-filter to git filter-branch.