Git branch in vanilla zsh

Recently the thought of having the current branch indicated on my zsh prompt hit me, when I looked up for solutions, I was greeted with the idea of installing one of the frameworks for zsh which obviously was not my cup of tea. I then looked up for other solutions which sort of worked but sometimes broke unexpectedly. I came up with a simple solution that has been working great for me for the past month or so in my vanilla zsh setup.

When I say vanilla zsh, I meant to say we are not going to use any of the fancy frameworks available for zsh namely oh-my-zsh or prezto. I personally avoid using such frameworks that add unnecessary overhead to your tool wherein the functionality you’re seeking can easily be added via simple configurations. One thing to note here is that we are just talking about having our current working branch displayed in our zsh prompt, if you are looking for a more sophisticated git integration, take a look at prezto, oh-my-zsh or read about the vcs_info package offered by zsh here.

Note: If you are just looking for the solution, jump to Conclusion directly and read on if you don’t mind bits of interesting info thrown around.

Git branch

Before I started looking for solutions to this particular problem, I only knew one way to echo the current branch in a directory which is the good old git branch command. But turns out there’s one more and possibly others.

$ git symbolic-ref HEAD

From the official documentation, git symbolic-ref <name> reads which branch head the given symbolic reference refers to and returns the path to it relative to the .git directory. In other words, when you give HEAD as an argument to git symbolic-ref, we could figure out the name of our current branch.

$ git symbolic-ref HEAD
refs/heads/master

I’m using the latter version since it will give us a rather brief and static output than git branch which would list all the branches there are in your current working tree.

Suppressing errors

In directories which are not git repositories, our command will throw an error. To supress such errors, we could simply redirect the error. Our updated command:

$ git symbolic-ref HEAD
fatal: Not a git repository (or any of the parent directories): .git

$ git symbolic-ref HEAD 2> /dev/null
$ 

The 2> /dev/null redirects the stderr or standard error to a special file /dev/null which takes input but doesn’t really do anything with it. So we’re sorted here. Read more about standard streams here.

Comes in awk

You certainly don’t need ref/heads/master in your prompt, let’s filter the unwanted stuff out. We’ll use a simple awk script (command really) to do the job.

$ git symbolic-ref HEAD 2> /dev/null | awk 'BEGIN{FS="/"} {print $NF}'
master

In the awk command above, first of all we specify the field separator (FS="/") since our git command returns a path which is separated by a forward slash and finally we print the last column in the separated list. $NF here means the number of fields and subsequently points to the last column. Now that we have our output sanitized, let’s get this onto our prompt.

Updating prompt

Now that we have all the inputs ready, let’s put these together to get it working. Add this function in your .zshrc, preferably on the top so that it becomes easier for you to re-use it.

function git_branch() {
    branch=$(git symbolic-ref HEAD 2> /dev/null | awk 'BEGIN{FS="/"} {print $NF}')
    if [[ $branch == "" ]]; then
        :
    else
        echo ' (' $branch ') '
    fi
}

Here, we initialize a branch variable with the value of the output of the command we put together in the steps above. If you are wondering why we have the command enclosed inside $(), this is called command substitution wherein a command is replaced by it’s output. So we’ll be left with the actual branch name in the variable branch. The conditional logic after that is used to handle cases where the current directory isn’t really a git repository and in which case we want the prompt untouched.

setopt prompt_subst
PROMPT='%~ $(git_branch) >'

Here, we set the prompt_subst option in our zsh, this allows command substitution to be able to be performed in prompts. In other words, when we defined the function git_branch above, we actually defined a custom command named git_branch which is used in our shell prompt since functions in shell scripts are essentially commands that can be executed from the shell. Now the shell performs command substitution everytime the prompt appears on the terminal. After this we set the prompt using the PROMPT shell variable. The %~ will be expanded to the current working directory. Read more about prompt expansions in zsh here.

Finally, source your .zshrc file to see the changes take effect. Your prompt should look like this assuming you are inside a directory which is a git repository and is on the master branch. This is how it looks on my machine.

drawing

Conclusion

So, having the current branch displayed on your zsh prompt was all in all a simple git command with a pint of awk in it and an even simpler shell script. For those restless souls who landed here in search of the solution, here it is.

# function to return current branch name while suppressing errors.
function git_branch() {
    branch=$(git symbolic-ref HEAD 2> /dev/null | awk 'BEGIN{FS="/"} {print $NF}')
    if [[ $branch == "" ]]; then
        :
    else
        echo ' (' $branch ') '
    fi
}


setopt prompt_subst             # allow command substitution inside the prompt
PROMPT='%~ $(git_branch) >'     # set the prompt value