Zsh Prompt Editing

March 14, 2023 | 4 Minute Read

I finally switched my default shell on my laptop (Mac) from bash to zsh. I’d never bothered tinkering with a more sophisticated shell before this, so it was interesting to figure out what zsh could do. But I was frustrated because I had a nice prompt in bash, and it took me a while to recreate it.

My bash prompt was pretty simple, it included my current directory, then my git branch, then status indicators for different types of dirty state in a git repo (specifically, staged vs. unstaged changes). It also used to have a unicode crown emoji, but after working with bash on a lot of hosts with older versions of bash that didn’t do well with unicode, I’d pulled the crown out years ago. (I was hopeful that I could add it back in, at least for my personal computer!)

(Sidenote: I looked into oh-my-zsh and then decided it was too complicated as a framework for my needs, so I’ll be ignoring it here.)

Replicating my current directory with color-coding was very easy in zsh. It was actually even easier than in bash, since zsh accepts some strings for colors rather than codepoints. After reading the zsh prompt expansion docs and this 2019 blog post about customizing your zsh prompt, I ended up with:

PROMPT="%B%F{magenta}%1/%f%b 👑 "

Here I initiate bolded and magenta-colored text (%B%F{magenta}), then print one directory out of my working directory, using an absolute path regardless of whether I’m inside my home directory (%1/), then undo the magenta color and bolding (%f%b).

Next I wanted to replicate the git-related part of my bash prompt. Here zsh is, again, more sophisticated than bash, and has a bunch of basic out-of-the-box git functionality. If you just want to display your branch name and/or dirty state, zsh can do it right out of the box. I found git’s own documentation of how to display git info in the zsh prompt super helpful, and it also linked directly to another section of the zsh docs on zsh and version control systems. After some trial and error (and more help from other people’s blog posts), I had this:

# grab current branch and display in prompt
# source:
autoload -Uz vcs_info add-zsh-hook
precmd_vcs_info() { vcs_info }
precmd_functions+=( precmd_vcs_info )
setopt prompt_subst

# These lines are specifically for staged + unstaged changes
# source:
add-zsh-hook precmd vcs_info
zstyle ':vcs_info:*' check-for-changes true
zstyle ':vcs_info:*' unstagedstr ' *'
zstyle ':vcs_info:*' stagedstr ' +'

zstyle ':vcs_info:git:*' formats '(%b%u%c)'

PROMPT='%B%F{magenta}%1/%f%b ${vcs_info_msg_0_} 👑 '

This did everything described above (show the git branch and all dirty states using different symbols), which was almost what I wanted. But I also really wanted part or all of the git part of my prompt to be color-coded red if there was any type of dirty state. After some spelunking through the git and zsh documentation, I decided that vcs_info was neat but just didn’t have enough power to allow me to conditionally format the magic vcs_info_msg_0 variable. So I switched tactics, and went back to an old and reliable standby: the script in the git repo itself.

I’d used this script before, to do the same things in bash, but I hadn’t yet installed or used it with zsh. So I explicitly included that in my .zshrc:

source ~/

And then I did something I’ve honestly never done before, and I went and read that script’s whole dang docstring to figure out if there was an easy way to do what I wanted. And there was! Here’s the final draft of my prompt, which felt very simple in the end:

source ~/

# allow prompt substitution, show dirty state in color (incl. untracked files), define prompt
# source: the (above) docstring
setopt prompt_subst
precmd () { __git_ps1 "%B%F{magenta}%1/%f%b " "👑 " "| %s " }

(Second sidenote: I did switch from assigning to PROMPT to using precmd () here because the docstring recommended it as faster, but I’m not convinced it’s faster for me. I haven’t looked into whether this is user error, or zsh being different, or something else I haven’t thought of.)