How to make Git pre-commit behavior depend on commit message?

Question

I know that to make git check the commit message before committing you can implement hooks/commit-msg. But now imagine a case where you want to let the hooks/pre-commit script behave differently based on the commit message?

For example (in a very loose environment) you might want to check whether you have a [nocheck] tag in your commit message which always lets your commit-check pass.

Or - in a more strict environment - you might want to have every file commented (and thus listed separately).

Or you might want to check the ticket ID against the related files.

etc...

Is there a way to accomplish this apart from doing the actual check in commit-msg (which seems to be counter-intuitive)?

Answer 1

But now imagine a case where you want to let the hooks/pre-commit script behave differently based on the commit message?

This is not possible because there is no commit message when it is fired ...

The pre-commit hook is run first, before you even type in a commit message.

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Is there a way to accomplish this apart from doing the actual check in commit-msg (which seems to be counter-intuitive)?

The way to do it is precisely using commit-msg :

The commit-msg hook takes one parameter, which again is the path to a temporary file that contains the current commit message. If this script exits non-zero, Git aborts the commit process, so you can use it to validate your project state or commit message before allowing a commit to go through.