Customizing your shell

Table of Contents

• Which terminal should I use?
• What font should I use?
• What shell should I use?
• Configuring your shell
• Configuring your prompt
• Shell configuration frameworks

Customizing your shell

It is very common for programmers to tweak and customize their terminal and shell for hours, add or write new plug-ins, all in pursuit of the “perfect environment” and an increase of productivity. Others, on the contrary, avoid tweaking their shell altogether in order to always get the same experience on every machine.

On a personal note, I tend to favor having a personalized shell as much as possible. I feel that sharing files between different computers is now a solved issue, and the benefits I get from having personalized my work environments are so great that I gladly pay the small price of synchronizing that configuration between my computers.

In that chapter, we will learn more about the shell and how to configure your terminal environment to make it work for you. Please note that some of the recommendations come from personal taste, and might not work for you nor suit you. We encourage you to explore and find what feels right, but we hope to at least nudge you in the right direction.

Which terminal should I use?

First off, if you are new to using the terminal, you might not have realized that it exists multiple terminal applications. MacOS comes with Terminal pre-installed, and most Linux distributions come with either xterm, Gnome-terminal or Konsole pre-installed, and there is a vast number of available alternatives.

I don't think there is a good, absolute and definitive answer when it comes to picking the “right” terminal application. You might get various answers depending who you ask. That being said, I can at least mention my own personal recommendations and preferences.

Whatever terminal you end up using, I think that it is really important you configure it to your liking and preferences. As a programmer, you will probably spend a great deal of time in your terminal, and for you to feel productive and empowered, it needs to work for you.

Terminator

If you are running Linux, I personally favor Terminatorover the default choices. It has several features I find useful:

• a tab system, allowing you to have multiple tab of terminal(s) within the same window
• a grid system, allowing you to have multiple terminals in the same tab

I can work in multiple panes within the same tab, and have one tab per project

Here are the terminator keyboard shortcuts I find the most useful:

iTerm2

As far as macOS is concerned, I find the default terminal (plainly named Terminal) to be hard to use. The terminal that seems to be widely accepted by the macOS programming community is iTerm2. It has all of the features cited above, and many (many) more!

iTerm2 looks similar to Terminator but can do much, much more

The iTerm2 keyboard shortcuts I find the most useful are:

The following sections go over some non-default iTerm2 settings that I find convenient. Again, these are my preference and are in no way prescriptive. Feel free to discard them if you want.

Open file shortcut

One of the iTerm2 features I enjoy is the ability of using Cmd + mouse click on a file path or an URL, to open the resource with the default associated program. For example, it will open an URL in your browser, a path to a local PDF file with Preview, a text file with your preferred text editor, etc.

By enabling this feature, you will be able to open a file using a graphical application from your terminal

Intuitive location for new terminals

Another tweak I've done to iTerm2 was changing the working directory new terminals will open into by default. What I wanted was

• open a new terminal window in my home directory
• open a new terminal tab in my home directory
• open a new terminal split pane in the previous session's directory

I did this because I oftentimes found myself splitting the current tab when I want to run multiple commands within the same project, and I had to cd into the project directory every time I did a pane split.

I reduced the time I spent cd -ing into project directories with these settings. Preferences > Profiles > General > Working Directory > Advanced Configuration > Edit

What font should I use?

Using a font you enjoy is paramount. If you spend a lot of time reading and writing in your terminal, you might as well do it using a font that feels right to you.

I personally really enjoy the Fira Codefont, both in my text editor and my terminal. Not only does it look really nice on the eye, but it also contains a set of ligatures for multi character combinations, such as ! and = rendered in a single character, allowing you to read code and decode symbols more easily.

Example of rendered character ligatures

Note that not all terminals support fonts with ligatures. For example, iTerm2 does but Terminator does not.

While Fira Code has my preference, there are other well-designed fonts including ligatures, such as JetBrains Mono.

What shell should I use?

We have hinted at it until now: bash is not the only shell out there. You are free to use other shells if you want, such as zsh , fish , nushell , … As it was the case with terminals, the “good” terminal really depends on your definition of “good”. If you deeply care about using the same shell on every machine you work on, then bash is possibly for you. It has been around since 1989, is stable, mature and is the default shell on almostevery UNIX system out there.

When researching this book, I was surprised to learn that zsh (or the Z-shell) wasn't really the last “kid on the block” either, as it was first released in 1990, just a year after the first stable bash release! You can expect the same level of stability, maturity and even syntax (to a large extent, except when it comes to configuration) than bash.

I personally think zsh really shines by providing a powerful default auto-completion experience, as well as more configuration options. As zsh is compatible with bash 's own syntax, I encourage you to try them until you feel comfortable with one or the other.

The fish shell takes a radical turn from bash or zsh by providing an incompatible but “simple and clean” syntax, an extremely powerful command suggestion system, and an interactive configuration wizard.

If you are getting started with using the shell, my personal recommendation is to stick to bash or zsh and experiment with other shells to see what value they bring once you feel more confident.

Changing your default shell

The chsh (standing for change shell ) command allows you to change your default shell.

Examples:

# Switching to bash by default
$ chsh -s /bin/bash

# Switching to zsh by default
$ chsh -s /bin/zsh

Once you have run chsh , any new terminal window you open will run your new default shell.

Configuring your shell

Up until now, every example we have seen have defined environment variables, aliases and functions directly in the shell. However, if we closed that shell, all of these changes would be undone and we would have to start again the next time we open a new one. Fortunately, all of these settings can be persisted in a configuration file . Adding aliases, environment variables and functions to that file will make sure they get imported every time you open a new shell.

These files usually reside in your home directory, and are named .bashrc for bash, and .zshrc for zsh.

$ cat ~/.zshrc
export EDITOR=vim
export PATH=$HOME/bin

alias ls='ls -G'
alias ..='cd ..'
alias ...='cd ../..'
alias filesize='ls --size --human-readable -1'

function mkcd {
    local target=$1
    mkdir -p "$target"
    cd $target
}

After adding anything to your shell configuration file, you need to run source ~/.zshrc (or source ~/.bashrc , depending on your shell). The source built-in command reads and executes commands from the argument file name in the current shell environment. Said in another way, running source ~/.<file> will cause the shell to reload its configuration.

rc stands for run commands . Indeed, when you source your configuration file, you will run the commands it contains. The subtlety with source is that it executes the argument script within your current shell, meaning any sourced commands will have a side-effect on your running shell.

If you can never remember a given command's options, or if you always find yourself typing a group of commands, I encourage you to define aliases and functions in your shell configuration file. They will allow you to feel more productive day after day, especially so if the alias and tools are abstracting complex commands.

The previous chapter ended with some real-life examples of alias and functions. Feel free to add them to your shell configuration file.

Configuring your prompt

Configuring your prompt is a very good way to make the shell work for you as much as possible, by providing you with useful context, such as the time of day, whether the last command was successful, your current working directory… While they can provide context and information to you, they will carry that context to anyone you copy and paste a command and associated output to.

Configuring your prompt is done by changing the value of the PS1 environment variable.

$ export PS1="MY COOL PROMPT $"
MY COOL PROMPT $

I think we can agree that MY COOL PROMPT is not as informative as it could, so let's change it to put our prompt to work. As the prompt configuration work slightly different between bash and zsh , we will address both cases in two different sections.

Configuring your bash prompt

The PS1 environment variable can be defined by using a mix and match of both regular and special characters. The regular characters are just displayed as-is, whereas the backslash-escaped special characters are interpreted by bash at the time PS1 is displayed and replaced by the associated value. The most useful special characters are defined as follows.

These special characters are evaluated every-time the prompt is displayed to make sure you always get the most up-to-date context.

The PROMPTING section of the bash manual contains the full list of backslash-escaped special characters.

Examples

$ export PS1='\u@\h \W $'
br@morenika ~ $

$ export PS1='[\t] \u@\h \W $'
[13:33:55] br@morenika ~ $

$ export PS1='[\t \u@\h:\w]\n>>> '
[13:57:55 br@morenika:~/code]
>>>

You can use online tools such as ezpromptto try different configurations until you find something you like.

Whatever PS1 value you settle with should be persisted and exported in your .bashrc configuration file.

Configuring your zsh prompt

zsh exposes a bit more options than bash when it comes to prompt configuration. Both PS1 and PROMPT environment variable can be set to the same effect, if you find PROMPT more explicit.

Instead of being backslash-escaped, zsh's special characters are prefixed by % , and are called prompt sequences . The most useful are detailed here.

You will find the full list of prompt sequences in the zsh documentation.

Examples

$ export PROMPT='%n@%m %~ $ '
br@morenika ~/code $

$ export PROMPT='[%*] %n@%m %~ $ '
[23:38] br@morenika ~/code $

$ export PROMPT="[%* %n@%m %~]"$'\n'">>> "
[23:41 br@morenika ~/code/izk]
>>>

$ export PROMPT="[%* %n@%m %1~]"$'\n'"%% "
[23:41 br@morenika izk]
%

zsh goes even further by letting you define the content of a right-sided prompt, through the RPROMPT environment variable, which uses the same syntax as PROMPT .

Example

$ export PROMPT='%~ $ '; export RPROMPT='%*'
~/code $                                              21:04:00

To make sure your changes are persisted, PROMPT and RPROMPT should be exported in your .zshrc configuration file.

Adding Colors

Adding color is a good way to spice up your prompt as well as providing some visual context. You can use color to indicate whether you are running with super-user privileges, if the last command succeeded or failed, or simply colorized each individual part of your prompt (username, hostname, etc) in a different way to make it even simpler to parse.

Adding color to your bash prompt

Bash allows you to style elements of your prompt by using 3-bit ANSIcodes defining a zone associated with a potential effect, foreground color and background color.

Each effect, background or foreground color has an associated code, described in the following tables. The combination of these parameters is called Select Graphic Rendition , which is defined as a semicolon (;) separated list of codes.

Examples of SGRs

34
1;32
35;47
1;31;106
1;9;33;42

To define colorized zones in your bash prompt, use the following (granted, ugly) syntax:

\e[<SGR>mTEXT\e[m

Examples

$ export PS1='[\t] \u@\h \W \e[32m$\e[m '

The $ sign is now displayed in green

$ export PS1='\e[31m\u\e[m@\e[32m\h\e[m \e[36m\W\e[m $ '

The username is in red, the hostname in green and the path is in cyan.

Color palettes

Notice how an ANSI code only maps to a color name? That's because it is up to your terminal to interpret and render that color name into an actual color, meaning that the same prompt configuration could be rendered differently on two different terminals.

Mapping ANSI color names to actual RGB colors is done through what is called color palettes .

Following are two different color schemes, as well as the associated rendered prompt, both using the same PS1 value, used in the previous example.

The popular Solarized Dark color scheme

The Pastel (Dark Background) color scheme

As you can see, these both look quite different from the prompt displayed in the previous screenshot , even though the underlying prompt configuration is exactly the same. This means that, even if using 16 colors can feel limiting, you actually can map these colors to any color you like. The ANSI color system just prevents you from having more than 16 different colors in your prompt.

I recommend you to have a look at the mbadolato/iTerm2-Color-Schemes project, showcasing popular color palettes and providing you with the configuration files allowing you to used them in many terminal applications (and not just iTerm2 contrary to what its name suggests).

Up to 256 colors

As computers eventually started to have 256 colors graphics card, a 8 bit ANSI code scheme was introduced, allowing the user to render 256 colors in their terminal, instead of 16.

The 8-bit ANSI code syntax is \e[38;5;n where the colors associated with each value of n between 0 and 255 are represented in the following table.

The 8-bit ANSI code allows you to render more than the initial 16 available colors

Examples

# Using 256-bit ANSI codes
$ TIME="[\e[38;5;33m\t\e[m]"  # blue
$ USERNAME="\e[38;5;200m\u\e[m"  # pink
$ HOSTNAME="\e[38;5;139m\h\e[m"  # purple
$ WORKDIR="\W"  # no color
$ DOLLAR="\e[38;5;41m$\e[m"  # green
$ export PS1="${TIME} ${USERNAME}@${HOSTNAME} ${PTH} ${DOLLAR} "

These ANSI codes sure are awful to read but they make for pretty colors

Not all terminals support 256 colors, but most of the modern ones should. To this day, GNOME Terminal, Konsole, Terminator, XFCE4 Terminal, iTerm2, Terminal (macOS) and tmux all support 256 colors.

Contrary to the 3-bit ANSI codes, the 8-bit codes are insensitive to color schemes changes, as shown in the following examples, both re-using the same PS1 configuration than in the previous screenshot .

The colors remain unchanged

Adding color to your zsh prompt

Everything we've explained in the previous section is still valid for zsh : you can use 3 or 8 bit ANSI color codes just fine. However, zsh also provides you with a much easier and readable color system:

• each color can be represented as either black , red , green , yellow , blue , magenta , cyan or white , or a number between 0 and 255
• %F{color}Text%f : changes the Text foreground color to color
• %K{color}Text%k : changes the Text background color to color
• %BText%b : displays Text in boldface
• %UText%u : underlines Text

Example

The current working directory in blue and the dollar sign in bold pink

Displaying dynamic data in the prompt

We can make our prompt display dynamic context to make it even more informative. To do this, we can execute a function as part of our PS1 environment variable. The shell will call that function every time it renders the prompt.

The idea is to be able to have as much information as possible in your prompt at the ready, but only when necessary .

Displaying dynamic data in bash

Let's say that we want to colorize the $ of our prompt in green if the last command was successful, and in red if it failed. We can wrap that logic into the following colorized_prompt bash function, and have it called every time PS1 is rendered by including $(colorized_prompt) in the environment variable.

The $(colorized_prompt) syntax means "call the colorize_prompt function", and will be expanded into the output of the function (what it prints), which will contain ASCII color codes colorizing the prompt.

function colorized_prompt {
    # Check if last command exit code equals 0
    if (($?)); then
        printf "\e[32m$\e[m"
    else
        printf "\e[31m$\e[m"
    fi

}
export PS1='[\t] \W $(colorized_prompt) '

$ pwd
/home/br
$ echo $?
0
$ cmdnotfound
bash: cmdnotfound: command not found
echo $?
127

The prompt is green after a successful command and red after a failed one

Displaying dynamic data in zsh

Dynamic data can be injected in your prompt the same way than in bash, by executing functions at rendering time. zsh however provides you with ternary conditionals , that is to say expressions that either evaluate to one value or the other depending on a condition, to reach the same goal. A ternary conditional has the following syntax

%(<condition>.<success value>.<failure value>)

If the condition is true, then the expression is evaluated to the success value. On the other hand, if the condition is false, the expression will be evaluated to the failure value.

You can read a ternary conditional as if condition, then, else . It's actually a common pattern called ternary expression you might encounter in many programming languages.

Here is a list of useful built-in conditions provided by zsh .

Examples

$ export PROMPT='%F{%(0?.green.red)}$ %f'

Displays a dollar prompt in green if the last command was successful, or red if it failed

$ export PROMPT='%* %1~ %(!.#.$) '

Display a dollar sign if you run your regular user, and a hash if you are running in super-user mode

The full list of ternary conditionals is available in the zsh documentation.

Adding emoji to your prompt

Modern terminal support non-ASCII characters, such as emoji. Like colors, they can be convenient to convey information in a very space-efficient fashion.

For example, during the process of writing that book, I displayed the associated total word count in my prompt to keep me motivated. That word count would however only be displayed when I was located in the root directory of the project, in the spirit of only displaying context when necessary.

Shell configuration frameworks

Up until now, we have seen how to tailor your prompt by adding colors, context, dynamic information computed on-the-fly. While you can certainly spend hours customizing up to “perfection” (trust me, I have been there…), you can also take another route and benefit from other people's work, using a shell configuration framework .

These frameworks provide you with a large choice of prompt themes, helpers, options, additional command auto-completions, plug-ins, and are regularly updated by a community of developers around the world.

To this day, the most famous zsh configuration frameworks are Oh My Zshand Prezto.While we can't fully attribute zsh 's success to them (Oh My Zsh was first released around 2010, 20 years after zsh's first release), they certainly have helped in driving community adoption in the last couple of years.

Comparison of Google Trends associated with zsh and Oh My Zsh

We will introduce you to the concepts behind Oh My Zsh, but it will then be up to you to explore, and select a theme as well as plug-ins you like (or even not use them at all!). After all, it is your development environment, and henceforth, your choice.

bash has a similar framework, inspired by Oh My Zsh, called bash-it .We won't cover it in details but we encourage you to look at it if don't feel like using zsh but still want to use a configuration framework.

Oh My Zsh

Quoting the official website,

Oh My Zsh is a delightful, open source, community-driven framework for managing your Zsh configuration. It comes bundled with thousands of helpful functions, helpers, plug-ins, themes, and a few things that make you shout…

To install it, run the following command in a shell, which will download an installation script, and run it on your computer.

$ sh -c "$(curl -fsSL https://raw.github.com/ohmyzsh/ohmyzsh/master/tools/install.sh)"

Once the script has finished running, you should see a message stating that Oh My Zsh has been installed, and that plug-ins, themes and options should be enabled by changing the configuration living under ~/.zshrc .

Before, we do, let's inspect our environment variables, to see how Oh My Zsh configures itself.

$ printenv | grep ZSH
ZSH=/home/br/.oh-my-zsh

That ZSH environment variable points to the Oh My Zsh installation directory. The framework also injected a couple of other variables defining specific configuration values.

$ set | grep ZSH
ZSH=/home/br/.oh-my-zsh
ZSH_ARGZERO=zsh
ZSH_CACHE_DIR=/home/br/.oh-my-zsh/cache
ZSH_COMPDUMP=/home/br/.zcompdump-morenika-5.7.1
ZSH_CUSTOM=/home/br/.oh-my-zsh/custom
ZSH_EVAL_CONTEXT=toplevel
ZSH_NAME=zsh
ZSH_PATCHLEVEL=zsh-5.7.1-0-g8b89d0d
ZSH_SPECTRUM_TEXT='Arma virumque cano Troiae qui primus ab oris'
ZSH_SUBSHELL=1
ZSH_THEME=robbyrussell
ZSH_VERSION=5.7.1

Picking a theme

We can see that the default theme is robbyrussell (Robby Russellis the creator of Oh My Zsh). The full list of available themes is available online, along with screenshots.

You can also get the list by running the following command, as all themes are defined in $ZSH/themes .

$ ls -1 $ZSH/themes | sed 's/.zsh-theme//'
3den
adben
af-magic
afowler
...

I suggest you scroll through the themes wiki, or simply pick a theme at random from the previous command output, edit your ~/.zshrc configuration file by updating the value of the ZSH_THEME variable, and run source ~/.zshrc to reload it. That will get you a whole new shell theme!

Feel free to rinse and repeat until you find a theme that suits you. In the case where no built-in theme finds grace in your eyes, you can also explore the external theme wiki. If you find an external theme you like, download its associated .zsh-theme file, and place it under $ZSH/themes , then edit ~/.zshrc , and update the ZSH_THEME accordingly.

$ mkdir -p $ZSH/custom/themes
$ cp $ZSH/themes/$ZSH_THEME.zsh-theme $ZSH/custom/themes/$ZSH_THEME-custom.zsh-theme

Useful configuration options

Oh My Zsh has a couple of options you can enable or disable by editing ~/.zshrc . I suggest you take a look at them and choose what to activate. Here are some personal recommendations.

Automatic command correction

zsh can suggest a command correction if it detects a mistyped command. To enable the automatic command correction, add ENABLE_AUTO_CORRECTION='true' to ~/.zshrc .

$ sl
zsh: correct 'sl' to 'ls' [nyae]? y
Android                bin   Desktop    Downloads  Firefox_wallpaper.png  Pictures
AndroidStudioProjects  code  Documents  Dropbox    Music                  Videos

The 4 options are:

n
y
a
e

alias git status='nocorrect git status'

Automatic Oh My Zsh updates

To make sure you regularly get new plug-ins and bug fixes, Oh My Zsh can automatically and regularly update itself. To do so, set the following options in ~/.zshrc :

DISABLE_UPDATE_PROMPT=true
UPDATE_ZSH_DAYS=30

Add plug-ins

Oh My Zsh comes with more than 250 plug-ins, each of them either defining aliases or improved auto-completion for a given set of commands. Refer to the Oh My Zsh wiki pageto see the full list of available plug-ins. To enable a given plug-in, add its name to the plugins list in ~/.zshrc , then run source ~/.zshrc .

Example:

- plugins=(git)
+ plugins=(git python)

If you regularly use a command listed in the plug-in wiki page, you should probably try to enable the associated plug-in! I however suggest enabling the following general-purpose plug-ins.

• common-aliases : Collection of useful aliases, not enabled by default since they may change some user defined aliases
• colored-man-pages : colorize man pages

Colorized man pages are much easier to read!

• extract : define an extract alias that can extract any type of archive (.zip, .tar.gz, .bzip, etc)

The following plug-ins are not provided by default, I find them so useful that I suggest you install them and give them a try.

• zsh-autosuggestions : emulate the fish autosuggestion by suggesting commands as you type them, saving you from using Ctrl - R to look into your shell history. Any suggestion can be accepted by hitting → or ignored by just continuing typing.

I just typed ls and I immediately get a completion suggestion

Suggestion accepted!

• zsh-syntax-highlighting : provide syntax highlighting within the zsh command line. It also colorizes the name of the command you type in green if it is found, and in red if not.

ls is a valid command

cmdnotfound is not

Uninstalling Oh My Zsh

If you find that Oh My Zsh isn't for you, you can uninstall it by running the uninstall_oh_my_zsh function. Your previous configuration will be restored.

Summary

I strongly believe that learning how to configure and personalize your own shell is an important part of becoming a developer. I'd even go as far as calling it a ritual. On a personal level, it helped me overcome the almost mystic reputation of the terminal by making it my own.

Configuring your shell might never really be fully completed. Do you find yourself executing a long command repeatedly? Make it an alias. If an alias does not cut it, or if it should take arguments, write a shell function instead. Are you oftentimes wondering on which branch, project or profile you are currently running? Add it to your prompt. If your prompt starts to feel a little crowded, you might be able to condense it by using colors and emoji.

Making your own tools and customizing your shell is an investment, but it is also an inherent part of being a software developer, which will allow you to do more, faster, and will help you feel more at home in your shell. It's also quite a bit of fun!

Going further

4.1: Look into your terminal's preferences and try to change the color scheme, or remap ANSI colors to different RGB colors.

4.2: Try different fonts, such as Source Code Pro , Fira Code Pro , Inconsolata or Jetbrains Mono and pick the one you like most

4.3: Explore your terminal preferences, and experiment with different settings.

4.4: Try to change the colors of the different sections of your prompt