This hook is called after the pre-commit hook to populate the text editor with a commit message. This is typically used to alter the automatically generated commit messages for squashed or merged commits.

One to three arguments are passed to this hook:

• The name of a temporary file that contains the message.
• The type of commit, either
• message (-m or -F option),
• template (-t option),
• merge (if it’s a merge commit), or
• squash (if it’s squashing other commits).
• The SHA1 hash of the relevant commit. This is only given if -c, -C, or --amend option was given.

Similar to pre-commit, exiting with a non-zero status aborts the commit.