Git hooks

The pre-commit is a shell script that does not take any parameters.

It stops the commit if the exit code is not zero, so we should use this feature to communicate messages.

  #!/bin/sh

  if git diff --staged --name-only | grep -q helloworld; then
      echo 'on parle francais s.v.p' && exit 1;
  fi

The prepare-commit-msg is a shell script that takes three parameters.

The first argument is simply the .git/COMMIT_EDITMSG file.

We use this file to prepare the commit message that git will present to us.

The second argument communicates the way the commit is being done.

For example, its value is message when we use a flag from this non-exhaustive list of flags: --message, --file, --fixup, --amend.

The third argument is a commit sha that is provided given the correct context.

An example would be when we amend a commit, the original commit sha will be passed to the script as the third argument.

  #!/bin/sh

  echo "Modify $(git diff --staged --name-only | wc -l | tr -d ' ') files" > $1

The commit-msg is a shell script that takes only the .git/COMMIT_EDITMSG file as parameter.

We can use this to validate the commit message, and exit with a non-zero value to fail the commit.

  #!/bin/sh

  test $(cat .git/COMMIT_EDITMSG | head --lines=1 | wc -c) -lt 72

The post-commit is a shell script that does not take any parameters.

It's run after the commit is done and can be used for notification purposes.

  #!/bin/sh

  echo "Nice job on $(git rev-parse HEAD)!"