World Wide Mike

At my job we use git for version control, and I wanted to do a few things whenever we pushed changes to the main tree. It took me a little bit of effort to figure out how it works, and below are my notes.

The post-receive hook is called when the repository receives changes. Let’s assume I have a git repository on my development machine that is a clone of a public git repository on a server. Then, when I run git push in my local repository in order to push my commits to the public repository, the post-receive hook is called on the public repository on the server.

Email Notification

On Debian-based systems there is an example email notification post-receive hook in /usr/share/doc/git-core/contrib/hooks/post-receive-email. It’s also available online from the git repo on github in the contrib/hooks directory.

In the repository that will be receiving commits (the public repository on the server, in the example above), first we need to make the post-receive hook executable:

$ cd /path/to/git/repo/.git/hooks
$ chmod +x post-receive

Then we need to call the post-receive-email script from inside this post-receive hook. Open .git/hooks/post-receive with your favorite editor and make sure this line exists:

. /path/to/post-receive-email

Notice we’re not executing the post-receive-email script, we’re sourcing it.

Next, we need to tell git where to send the email to. The hooks.mailinglist property controls this:

$ cd /path/to/git/repo
$ git config hooks.mailinglist "mailinglist@example.com"

At this stage emails will be sent each time changes are pushed to the public git repository containing a summary of the new changes.

By default, emails refer to the project as “UNNAMED PROJECT”. To change this, edit .git/description.

For further customization options, look inside post-receive-email. For example:

$ cd /path/to/git/repo
# envelopesender? see `man sendmail` for the -f switch
$ git config hooks.envelopesender "git@example.com"
$ git config hooks.emailprefix "[MY PREFIX] "  # note the trailing space

Kicking Off a Buildbot Build

You may also want to have Buildbot start a build from the post-receive hook. Like the email script, the Buildbot git script expects revision hashes on standard input. The post-receive script then needs to be modified a little to pass the hashes it receives via standard input to all the scripts it invokes. Here’s a new copy of post-receive:

while read oldrev newrev refname
do
   echo $oldrev $newrev $refname | /bin/sh /path/to/post-receive-email
   echo $oldrev $newrev $refname | /usr/bin/python /path/to/git_buildbot.py
done

This script first reads oldrev, newrev, and refname from standard input, then pipes those values into post-receive-email and git_buildbot.py. We loop until there is no more input, presumably because another push may happen while we’re executing.