post-commit — Notification of a successful commit.
The post-commit hook is run after the
          transaction is committed and a new revision is created.  Most
          people use this hook to send out descriptive emails about
          the commit or to notify some other tool (such as an issue
          tracker) that a commit has happened.  Some configurations
          also use this hook to trigger backup processes.
If the post-commit hook returns a
          nonzero exit status, the commit will
          not be aborted since it has already
          completed.  However, anything that the hook printed
          to stderr will be marshalled back to the
          client, making it easier to diagnose hook failures.