Git post-receive for multiple remote branches and work-trees

A while ago I set up my server to automatically deploy new content from my git repositories when changes where pushed to them. This automatic workflow is great and fairly simple to setup, but I recently needed to add a twist to it: what if I want to deploy separate remote branches to their own individual work-trees? Here’s how…

Below is a walkthrough of my findings along the way of debugging the initial implementation, but if you’re in a hurry, you can go straight to the solution

Initial, single remote branch setup

The initial setup has been explained here before, so you only have to follow these basic instructions to get yourself going on a single master branch auto-deployment.

More branches, more work-trees please!

Right, now let’s say you want not only the master branch of your code to be deployed to a live website, but you also want the development branch to be deployed to it’s own web root directory so you can test a development version of your site (and potentially f** it all up) while the live site still runs the last “gold” version of your code. You will undoubtedly have several local branches, several corresponding tracking remote branches. For this setup, you will also need several corresponding work-trees, all with their automated deployments upon pushing to the main repository.

Unsurprisingly, there is very little to change to our method explained in the previous setup, but the basic instructions I found did not initially work on my Ubuntu server, so you’ll have to be aware of a few things.

Initial findings

Dylan over dylanserver.com posted this handy bit of code earlier this year:

  if ! [ -t 0 ]; then
    read -a ref
  fi

  IFS='/' read -ra REF <<< "${ref[2]}"

  branch="${REF[2]}"

  if [ "live" == "$branch" ]; then
    git --work-tree=/var/www/dylanstestserver.com/ --git-dir=.. checkout -f
    echo 'Changes pushed live.'
  fi

If you read carefully the post, you can notice that the checkout command is still there, but augmented with the –work-tree and –git-dir arguments.

Great! Thats a great starting point, firing up vi on my remote server, I edited my ‘post-receive’ hook and pasted the following code in it (after changing the branch name to “dev” instead of “live” to test only with my dev site). Note that I had also added the shebang at the top of the file…

  #!bin/sh
  if ! [ -t 0 ]; then
    read -a ref
  fi

  IFS='/' read -ra REF <<< "${ref[2]}"

  branch="${REF[2]}"

  if [ "dev" == "$branch" ]; then
    git --work-tree=/path/under/root/dir/dev-site/ --git-dir=.. checkout -f
    echo 'Changes pushed dev.'
  fi

The next git push executed the hook but I got the following error in the git push output:

read: 4: Illegal option -a

The right shebang

The problem was that the shebang I added uses sh, which, according to some stackoverflow answers doesn’t use bash on ubuntu (my server). Incidentally, I found this out after fiddling around with the read command and removing the -a option, only to find out that an “unexpected redirect” has been found.

The solution was simple: change the shebang to:

#!bin/bash

Now, that hook was going to checkout my dev branch into my development site’s root directory… err… Not quite yet.

The right git directory

The next error I encountered was:

fatal: Not a git repository: '..'

That’s from the script itself, but I can’t understand why this was failing, as –git-dir should accept absolute or relative directories. However, the GIT_DIR environment variable should be set to the current directory, which during the push, is the git directory. So I elected to remove the option altogether:

  #!bin/sh
  if ! [ -t 0 ]; then
    read -a ref
  fi

  IFS='/' read -ra REF <<< "${ref[2]}"

  branch="${REF[2]}"

  if [ "dev" == "$branch" ]; then
    git --work-tree=/path/under/root/dir/dev-site/ checkout -f
    echo 'Changes pushed dev.'
  fi

Now the push didn’t report any error, and “some” code to the correct development website root directory! Yay! BUT… That code was the MASTER branch’s code. Not the DEV branch.

The right solution

As all we are doing in the hook is performing a git checkout (with some options), we can simply pass the branch we want to checkout as a parameter and all works well! I’m yet to understand what environment variables are set and used by the hook, but for the moment, my final post-receive hook looks like this:

Edit - Thanks to Peter and his comments below, the script below now works while pushing multiple branches at once! Thanks to him!

  #!/bin/bash

  while read oldrev newrev ref
  do
    branch=`echo $ref | cut -d/ -f3`

    if [ "master" == "$branch" ]; then
      git --work-tree=/path/under/root/dir/live-site/ checkout -f $branch
      echo 'Changes pushed live.'
    fi

    if [ "dev" == "$branch" ]; then
      git --work-tree=/path/under/root/dir/dev-site/ checkout -f $branch
      echo 'Changes pushed to dev.'
    fi
  done

You will notice I have added the master branch in there too, and you can expand the script with whatever branch you want to checkout, along with the correct work-tree.