Website/content/blog/006-building-a-zsh-prompt.md

---
title: Building a ZSH prompt
tags:
  - Linux
  - ZSH
description: There are many frameworks out there to help you build a prompt, I thought I'd see how far I could get without one.
date: 2020-03-24
draft: true
---

Until recently, I was using [oh-my-zsh](https://github.com/ohmyzsh/ohmyzsh) with the [Power Level 9k](https://github.com/Powerlevel9k/powerlevel9k) prompt.

In part of my effort to understand how different parts of my system works, and to reduce my reliance on some libraries, I decided to see if I could get what I needed without them. In this blog post, I am going to focus on my prompt configuration.

If you want to follow along, my configuration can be found in [my dotfiles](https://github.com/Jab2870/dotfiles/blob/master/shells/zsh/includes/promptconfig.zsh).

My prompt currently looks something like this:

![My Prompt](/assets/prompt/prompt.png)

## Basics

Zsh simply prints the variables `PROMPT` and `RPROMPT` when drawing the left and right prompts respectively. `PROMPT` is roughly equivalent to the `PS1` variable in bash.

By setting the variable, you can change how the prompt works. E.g.

```
oldPrompt $ PROMPT="new prompt > "
new prompt > ls
Documents	Downloads	GitRepos
new prompt > █
```

## ZSH Hooks

Zsh has a concept called hooks. These allow you to run a function (or functions) automatically at certain times.

For the purposes of setting my prompt, I want to run a function to set `PROMPT` and `RPROMPT` before the prompt is drawn. This can be done with the `precmd` hook.

```zsh
set_prompts(){
	PROMPT="$ "
	RPROMPT=""
}
zle -N set_prompts
autoload -U add-zsh-hook
add-zsh-hook precmd set_prompts
```

This defines a function `set_prompts` and it will be run just before the prompt is drawn, every time. We can therefore use it to build the prompt.

## Drawing segments

I like the arrow style that was made popular by [Powerline](https://github.com/powerline/powerline). To achieve this, you will need a font that contains the powewline glyphs. If you don't have one, I highly recommend the [Nerd Fonts](https://www.nerdfonts.com/) project that aggregates a lot of icons as well as the powerline symbols. It even includes a script that allows you to add them to your favourite font.



## Exit Code

In ZSH (and most other shells), the exit code of the previous command is available in the special `$?` variable. If we want the exit code of the last command run, we need to assign this to a variable first.

```bash
# Get the return status of the previous command
local RETVAL=$?
```

## Git

I use Git a lot. It is useful to tell, at a glance, which branch I'm on, which tag I'm on and what the state of repository is. The function is quite simple:

```bash
prompt_git(){
	local repoTopLevel="$(command git rev-parse --show-toplevel 2> /dev/null)"
	if [ -n "$repoTopLevel" ]; then
		local branch="$(git branch --show-current 2> /dev/null)"
		local tag="$(git describe --tags --exact-match HEAD 2> /dev/null)"
		local color="green"
		local ret=""
		[ -n "$branch" ] && ret="$branch "
		[ -n "$tag" ] && ret+="$tag "
		[ -n "$ret" ] || ret="$(git rev-parse --short HEAD 2> /dev/null)"
		local repoTopLevel="$(command git rev-parse --show-toplevel 2> /dev/null)"
		local untrackedFiles=$(command git ls-files --others --exclude-standard "${repoTopLevel}" 2> /dev/null)
		local modified=$(command git diff --name-only 2> /dev/null)
		local staged=$(command git diff --staged --name-only 2> /dev/null)

		if [ -n "$untrackedFiles" ]; then
			ret+=" "
			color="orange1"
		fi
		if [ -n "$modified" ]; then
			ret+=" "
			color="orange1"
		fi
		if [ -n "$staged" ]; then
			ret+=" "
			color="orange1"
		fi
	fi
	ret="$(echo "$ret" | sed -e 's/ *$//')"
	echo "$ret"
	echo "$color"
}
```