Question

So my branch is named after bugtracker ticket number, something like “issue-1234”, and we have a convention to always write down ticket number in commit message. I’m wondering if it’s possible to append the ticket number in commit message automatically when I’m working on an issue-* branch without me explicitly typing it.

I looked at git commit hooks, namely pre-commit, prepare-message, and post-commit, and none of them seem to be able to do what I wanted. Post-commit hook comes close, but you cannot modify the message that’s committed with -m.

To reiterate, I’m wondering if this is possible:

On branch: issue-1234

git commit -a -m"fixed this pesky issue"

After the commit, in git log, it shows the message as:

fixed this pesky issue. ticket number: #1234

Answer 1

You missed a hook. The one you want is commit-msg:

This hook is invoked by git commit, and can be bypassed with –no-verify option. It takes a single parameter, the name of the file that holds the proposed commit log message. Exiting with non-zero status causes the git commit to abort.

So for example:

#!/bin/sh

ticket=$(git symbolic-ref HEAD | awk -F- '/^issue-/ {print $2}')
if [ -n "$ticket" ]; then
    echo "ticket #$ticket" >> $1
fi

That’s a very naive parsing of your branch name, and it’s simply appended to the commit message on its own line. Modify it if that’s not good enough for you.

Of course, I’d actually recommend doing this in prepare-commit-msg, and committing with git commit (without -m). It’s very, very rare that you can actually write sufficient information in a single-line commit message. Further, that will let you see the message before the commit is made, in case your hook doesn’t do quite what you want.