Personalize Zsh Prompt

In this post, I will highlight some of the ways in which you can manipulate the information displayed as part of the command prompt. The default shell in all Apple computers and laptops changed to zsh from macOS Catalina and onwards. Zsh is a specific type of shell just as macOS is a specific type of operating system. Other popular shell varieties include bash, cshell, powershell etc.

Oh My Zsh is the Zsh package manager which allows you to manage the different zsh configurations, plugins and themes to enhance the look and functionality of the Zsh shell.

Note: All the instructions are written and tested on macOS Monterey (v12.0.1).

Step 1: Install Oh My Zsh

You can check the type and version of the shell to confirm if you have zsh.

$ echo $SHELL
/bin/zsh
$ $SHELL --version
zsh 5.x

If you do not have zsh, you can get started with first installing it using one of many package managers. It is available on conda and can be installed using:

$ conda install -c conda-forge zsh

To set zsh as the default shell, run:

$ chsh -s /bin/zsh

Follow one of the methods listed in README for Oh My Zsh to install it.

Step 2: Customize configuration

The primary file you would work with is .zshrc located in your home folder ~. Since it is a hidden file, you can first check if this file exists.

$ ls -a ~

You can also open an empty document and copy the contents of the zshrc template file to get started.

Oh My Zsh offers many themes. Open the .zshrc using any text editor, update the value for ZSH_THEME to the one you prefer, save and exit. The default is set to robbyrussell. To get a local list of all the themes, run:

$ ls -a ~/.oh-my-zsh/themes

For the changes to take effect, you can either start a new terminal window or run:

$ source ~/.zshrc

Similar to the themes, there are a wide variety of plugins available. You can check the complete list on the Wiki page or locally using:

$ ls -a ~/.oh-my-zsh/plugins

Update the values in the plugins variable in the ~/.zshrc file to the ones you prefer. For example:

plugins=(git brew macos colored-man-pages)

Remember to save any changes you make to the configuration file and update the shell for the changes to take effect.

$ source ~/.zshrc

Step 3: Customize virtualenv information

Typically virtual environments prepend the command prompt.

(virtualenv) $

To be able to view this information on a Oh My Zsh theme, we need to follow a few steps. Go to the configuration file and add virtualenv to the plugins list.

plugins=(git brew macos colored-man-pages virtualenv)

At the end of the .zshrc file on a new line copy the following lines, save and exit.

function virtualenv_info {
 [ $CONDA_PROMPT_MODIFIER ] && echo `basename $CONDA_PROMPT_MODIFIER`
}

Note: The above function is specific to conda. Replace the CONDA_PROMPT_MODIFIER with VIRTUAL_ENV for all other virtual environment managers.

Next access the specific theme file. I am using pygmalion as the example.

 $ nano ~/.oh-my-zsh/themes/pygmalion.zsh-theme

Variables base_prompt and post_prompt are declared at the top of the file. Add a new variable to define the conda virtualenv information.

conda_env='%{$fg[magenta]%}$CONDA_PROMPT_MODIFIER%{$reset_color%}'

Scroll to the end of the page to find the prompt_pygmalion_precmd() function:

prompt_pygmalion_precmd(){
  setopt localoptions nopromptsubst extendedglob

  local gitinfo=$(git_prompt_info)
  local gitinfo_nocolor=${gitinfo//\%\{[^\}]##\}}
  local exp_nocolor="$(print -P \"${base_prompt_nocolor}${gitinfo_nocolor}${post_prompt_nocolor}\")"
  local prompt_length=${#exp_nocolor}

  PROMPT="${base_prompt}${gitinfo}${post_prompt}"  
}

Modify the PROMPT variable within the function to include the newly created variable:

  PROMPT="${conda_env}${base_prompt}${gitinfo}${post_prompt}"

Save and exit from the theme file. Subsequently update the shell by running source ~/.zshrc. The command will now display the virtualenv information along with all the previously displayed information.

(base) $

Step 4: Modify prompt without theme support

Although there are many themes, not all support the display of the virtualenv information by modifying the theme file as shown in Step 3. In those cases, you can define the prompt with all the information you would like displayed and add it to the ~/.zshrc file.

Note: You need to comment out the PROMPT variable in the theme file for the custom prompt settings to apply.

Add the following line to .zshrc file:

PROMPT='%{$fg[magenta]%}$(virtualenv_info)%{$reset_color%} %{$fg[cyan]%}%3~%{$reset_color%}|$(git_prompt_info)$ '

In zsh, % and ) are special characters. The fg signifies the foreground color. The %3~ shows the path of the current working directory at three levels depth. If you prefer the full path relative to the home directory to be shown you can update it to %0~. The (git_prompt_info) points towards the currently checked out git branch for the repository. Save and exit the .zshrc. To see the changes take effect, run:

source ~/.zshrc

Ultimately, there are many options to customize the command prompt to appeal to your aesthetic taste and to display the information you find most useful. Hopefully this post helps decode some aspects of it. Happy tweaking!