Git, a distributed revision control system, is steadily gaining momentum. For beginners, Git typically comes with its unique challenges, which we will probably address in a separate post. On the other side, Git comes with plenty of customization and integration options due to its excellent scriptability, which are a major plus in terms of developer productivity.

This post will outline how to activate one of those gimmicks: Tweaking the bash prompt to enable displaying information about the current Git repository, such as the current branch or whether there are any dirty (or untracked) files. These instructions are based on the assumption that you are running a recent Ubuntu release, such as the current Ubuntu 11.04. Ubuntu 10.10 will also do the trick, while the status of Ubuntu 10.04 is currently unknown to the author. The procedure for other Linux distributions (especially Debian) should be similar.

First, make sure that you have the git package (which may be named git-core for your distribution version) installed and also install the basic bash-completion package. While bash-completion is active on Ubuntu by default, you need to manually enable it on Debian by adding the following snippet to /etc/bash.bashrc, which is used by bash to initialize interactive shell sessions (in contrast to /etc/profile for non-login shells):

# Check for interactive shell.
if [ -n "$PS1" ]; then
  if [ $bmajor -eq 2 -a $bminor '>' 04 ] || [ $bmajor -gt 2 ]; then
    if [ -r /etc/bash_completion ]; then
      # Source completion code.
      . /etc/bash_completion
    fi
  fi
fi
unset bash bminor bmajor

Once this is in place, we are ready to enable Git integration. First, you will need to decide if you would like to enable that tweak just for the current user or whether you would like to enable it globally (chances are good that you will not notice any difference for a single-user system). In this configuration example, we will take the local route. If you would like to activate the tweak globally, just make the changes in /etc/bash.bashrc instead.

So, let’s get started: What is displayed as the bash prompt is determined by the current setting of the PS1 variable. On a stock system that may read:

PS1='\u@\h:\w\$ '

To figure out your system’s default, type

echo ${PS1}

at the prompt.

To enable Git integration, we will override the default setting by adding the following line to ~/.bashrc:

PS1='\u@\h:\W$(__git_ps1 " (%s)")$'

If you would like to get an indicator (“*”) for dirty changes, set the GIT_PS1_SHOWDIRTYSTATE variable as in:

GIT_PS1_SHOWDIRTYSTATE=1

Further available options are:

• GIT_PS1_SHOWSTASHSTATE: Shows an indicator (“$”) for a non-empty stash
• GIT_PS1_SHOWUNTRACKEDFILES: Shows an indicator (“%”) for a untracked files

That’s basically it. Save your changes to .bashrc and open a new shell. When changing into a directory hosting a Git repository, you should see the enhanced prompt as in (note the branch specification in braces):

user@host:dir (master)$

If you like things a bit more colorful, you may prefer this variant:

PS1='\[\033[01;32m\]\u@\h\[\033[00m\] \[\033[01;34m\]\W\[\033[01;33m\]$(__git_ps1 " (%s)")\[\033[00m\]\$ '

Enjoy!