I have paired a lot over the past week (which makes me tremendously happy!) and I noticed how lost I can get in someone else’s terminal if I don’t have my regular bash prompt - not only the cute little heart that welcomes me every time I run the terminal, but also the git branch name I’m currently on.

As I couldn’t find the tutorial I used to learn how to parse the git branch, I decided to go through my .bashrc and write one myself.

Bash prompt variables

Bash prompt variables hold the text that shows as the terminal prompt in various contexts. Their values are examined and executed just before Bash prints them. There are several of them, but for now I’m going to focus on PS1, which is the primary prompt string.

In a bash prompt, you can use:

  • special characters that can be used for current user name (\u), time (\t), host name (\h) etc.
  • colors both for the foreground and the background
  • unicode characters (letters, numbers, symbols, emoji)
  • custom variables

Let’s look at an example value of PS1: \s-\v\$

  • \s the name of the shell
  • - just a dash
  • \v the version of the shell
  • $ a dollar sign at the end of the prompt

which in my terminal evaluates to: -bash-3.2$

To change the value of PS1 for the current session, you can use export PS1="<value>" in the terminal:

  • adding a lambda 
    export PS1="λ "
  • changing the lambda’s color to red 
    export PS1="\[\033[0;31m\]λ \[\033[0m\]"
  • adding the current directory before the red lambda 
    export PS1="\w\[\033[0;31m\] λ \[\033[0m\]"

and so on.

If you want to make the PS1 more permanent, you can add it to your .bashrc (or .bash_profile, if you’re on a Mac), reload your session with

source .bashrc

et voilà!

Getting information from git

When I work on code, I usually want to know a few things:

  • am I using git? (if not, I might want to git init)
  • what branch I am currently on?
  • are there any changes in the directory - untracked, unadded, added or deleted files?

All of those things I can check by simply using the git status command, but it gets tedious to do that every time I need to change something (am I on the right branch? did I add everything? did I switch to a feature branch?). I can also parse git commands output with Bash and add the parsed information to my prompt, using custom variables.

Branch

In order to get the current branch, you can parse the output of several different git commands. I don’t think there is one good way to do it, as you might want to get slightly different results depending on the context, but some good ideas are:

  • git rev-parse --abbrev-ref HEAD - which gives you the right name of the local branch and consistent HEAD for other contexts
  • git branch | sed -n '/\* /s///p' - which gives you the right name of the local branch and appropriate outputs for other contexts

Whichever method you choose, to add it to your PS1 prompt you can:

  • add a function for parsing the branch (the 2>/dev/null stops the command from printing the output): 
    git_prompt() {
  local ref=$(git branch 2>/dev/null | sed -n '/\* /s///p')
  if [ "$ref" != "" ]
  then
    echo "($ref) "
  fi
}
  • add the function output to your prompt 
    export PS1="\w\[\033[0;31m\] λ $(git_prompt)\[\033[0m\]"

    or, with a hint of color

    export PS1="\w\[\033[0;31m\] λ \[\033[0;95m\]\$(git_prompt)\[\033[0m\]\[\033[0m\]"

Number of various changes

You can run git status with various options - if you use the short format, you will get the statuses of your paths that are a bit easier to understand for parsing purposes, notably:

  • ? for untracked paths
  • M for modified paths
  • A for added paths
  • D for deleted paths

To parse untracked paths you can:

  • grep git status --porcelain for ? and count the number of lines in the output (as each untracked path is on a new line) 
    untracked=`expr $(git status --porcelain 2>/dev/null | grep "?" | wc -l)`
  • wrap it in a function that returns the number of untracked paths with a symbol of your choice when it’s not 0 
    function parse_untracked {
  local untracked=`expr $(git status --porcelain 2>/dev/null | grep "?" | wc -l)`
  if [ "$untracked" != "0" ]
  then
    echo " ?$untracked"
  fi
}
  • add it to your PS1 prompt 
    git_prompt() {
  local ref=$(git branch 2>/dev/null | sed -n '/\* /s///p')
  if [ "$ref" != "" ]
  then
    echo "($ref)$(parse_untracked) "
  fi
}

You can add a separate function for each status and add them to your prompt by simply grepping for the appropriate symbol and wrapping it in a function. For reference, my full git parsing code is in this gist.

Have fun adjusting your prompt and hopefully never getting lost among your git branches!