brandon phillips

Shell, Yes!

For any Linux enthusiast, administrator, developer, systems engineer, or overall neck-beard, the terminal is the meat and potatoes of a good chunk of day-to-day work and interaction with Linux. Your terminal's shell is a powerful tool to make your work easier and more fun to work with.

Configuring your shell to work for your needs is a useful skill to have and is at the heart of automation in your terminal environment. We computer nerds are lazy and love tweaking computer environments to do work for us.

Anatomy

I'm going to break down shell configurations into several different files (more details in this awesome Unix StackExchange answer):

• rc - controls our shell's interactive behavior.
• env - contains exported environment variables.
• aliases - contains—you guessed it—our aliases.

There are a few other files, but I'll mention them later.

I use zsh as my shell, so this post will focus on it. The principles should stay the same for your shell of choice.

The rc file

An rc file (or a RUNCOM file) is a file or directory designated to hold configurations for an interactive shell. Modern shells usually come preinstalled with an rc file with several example configuration lines and inline comments explaining them, and these example files can vary between Linux distributions.

This is the best place to start your configurations, and there are plenty of experienced users out there who run their shell with all of its configurations in this file alone. The rc is arguably the most important config file for your shell. (The second most important is the file that makes it look cool.)

Let's start configuring this thing. We'll continue using zsh as our example here, and will pull the important lines from the generated zshrc that comes with a zsh install, as well as add a few of our own.

# .zshrc

HIST_STAMPS="mm/dd/yyyy"
ENABLE_CORRECTION="false"

if [ -f ~/.aliases ]; then
    . ~/.aliases
fi

eval "$(dircolors -p | \
    sed 's/ 4[0-9];/ 01;/; s/;4[0-9];/;01;/g; s/;4[0-9] /;01 /' | \
    dircolors /dev/stdin)"

function precmd {
    if ! typeset -f deactivate >/dev/null; then
        for activate in ./venv/bin/activate ./.venv/bin/activate; do
            if [ -e "$activate" ]; then
                . "$activate"
            fi
        done
    fi
}

if ! [[ -n $SSH_CONNECTION ]]; then
  if [ "$TMUX" = "" ]; then tmux; fi
fi

We'll break this down line-by-line:

• HIST_STAMPS="mm/dd/yyyy" describes the timestamp formatting for our shell history.
• ENABLE_CORRECTION="false" sets command-line autocorrection.
• The if block checks for our .aliases config file, and makes sure zsh sees it.
• The eval statement removes the background colors of directories when running ls commands.
• The function precmd will activate a venv when navigating to a directory that holds a venv.
• Lastly, the if block at the bottom will activate tmux when the shell is launched, as long as it's not over a ssh connection.

The env file

The env (environment) file contains our exported variables, we want to put variables that other programs will see or use in here. Some examples (from the previous StackExchange answer) include your $PATH, $EDITOR and $PAGER environment variables. The zsh .zshenv file is always sourced.

Here are some lines from my .zshenv file:

# .zshenv

export DOTFILES=$HOME/.dotfiles
export DOCKER=podman
export PATH=$HOME/bin:/usr/local/bin:$PATH
export LANG=en_US.UTF-8

# Preferred editor for local and remote sessions
if [[ -n $SSH_CONNECTION ]]; then
  export EDITOR='vim'
else
  export EDITOR='hx'
fi

First, we create a DOTFILES variable that describes the location of our dotfiles (I'll go over this later, but this is where we'll store our configs for backups and version control).

Next, I prefer to use Podman over Docker, so for convenience, I have the $DOCKER env variable point to podman instead.

Then, a line that adds $HOME/bin and /usr/local/bin to $PATH, then we set $LANG to en_US.UTF-8.

In the if block here at the end, we set $EDITOR to Helix if we're not on a ssh connection, and Vim if we are connected via ssh.

Now we'll take a look at the contents of the .aliases file we dropped into our .zshrc earlier.

The aliases file

This one will be brief, as everyone's aliases are very different from everyone else's. Most of my aliases are ssh commands to quickly jump to other hosts, but there's a few others that I use as well.

# .aliases

# grep
alias grep='grep --color=auto'
alias fgrep='fgrep --color=auto'
alias egrep='egrep --color=auto'

# cat
alias cat='bat --theme Nord -p'

# ls 
alias ll='ls -Al'
alias la='ls -A'
alias ls='ls --color=auto'
alias l='ls -CF'

# dir
alias dir='dir --color=auto'
alias vdir='vdir --color=auto'

# opening files in your $EDITOR
alias ali='$EDITOR ~/.aliases'
alias zrc='$EDITOR ~/.zshrc'

# source config files
alias arc='source ~/.aliases'
alias src='source ~/.zshrc'

# system updates (this is for rpm-based systems like Fedora)
alias upd='sudo dnf upgrade -y && flatpak update'

These are pretty straight forward. We use the alias keyword followed by a key-value pair describing our alias and the command it represents. The ls, grep, and dir aliases here can be copied and pasted without issue; the cat alias will require bat, a fancy cat alternative. The rest are shortcuts to open or source config files in the set $EDITOR (from the env file), plus one to run system updates on Fedora.

Zsh will read these as though they were directly in the .zshrc. I like to keep the aliases separate, it feels more organized to me, but there's no issue at all with dropping them straight into the rc if you like everything in one place. They will both work the same.

These examples work independently from one another; when you come across examples like these, try experimenting with them line-by-line, and work them into your own configuration, instead of dropping them all blindly in your config.

How Your Shell Loads Its Configs

If you want to segment out your config options, aliases, environment variables, functions, etc. into these separate files, then you should understand the order in which your shell loads them, to avoid any conflicts and redundancies.

These config files are really just scripts, like any other shell script, that are called when the shell is run or exited.

Here's how zsh will load its config files, from this great post:

+----------------+-----------+-----------+------+
|                |Interactive|Interactive|Script|
|                |login      |non-login  |      |
+----------------+-----------+-----------+------+
|/etc/zshenv     |    A      |    A      |  A   |
+----------------+-----------+-----------+------+
|~/.zshenv       |    B      |    B      |  B   |
+----------------+-----------+-----------+------+
|/etc/zprofile   |    C      |           |      |
+----------------+-----------+-----------+------+
|~/.zprofile     |    D      |           |      |
+----------------+-----------+-----------+------+
|/etc/zshrc      |    E      |    C      |      |
+----------------+-----------+-----------+------+
|~/.zshrc        |    F      |    D      |      |
+----------------+-----------+-----------+------+
|/etc/zlogin     |    G      |           |      |
+----------------+-----------+-----------+------+
|~/.zlogin       |    H      |           |      |
+----------------+-----------+-----------+------+
|                |           |           |      |
+----------------+-----------+-----------+------+
|                |           |           |      |
+----------------+-----------+-----------+------+
|~/.zlogout      |    I      |           |      |
+----------------+-----------+-----------+------+
|/etc/zlogout    |    J      |           |      |
+----------------+-----------+-----------+------+

If you use bash, here's a table describing the equivalent files and their load order in bash from the same post.

+----------------+-----------+-----------+------+
|                |Interactive|Interactive|Script|
|                |login      |non-login  |      |
+----------------+-----------+-----------+------+
|/etc/profile    |   A       |           |      |
+----------------+-----------+-----------+------+
|/etc/bash.bashrc|           |    A      |      |
+----------------+-----------+-----------+------+
|~/.bashrc       |           |    B      |      |
+----------------+-----------+-----------+------+
|~/.bash_profile |   B1      |           |      |
+----------------+-----------+-----------+------+
|~/.bash_login   |   B2      |           |      |
+----------------+-----------+-----------+------+
|~/.profile      |   B3      |           |      |
+----------------+-----------+-----------+------+
|BASH_ENV        |           |           |  A   |
+----------------+-----------+-----------+------+
|                |           |           |      |
+----------------+-----------+-----------+------+
|                |           |           |      |
+----------------+-----------+-----------+------+
|~/.bash_logout  |    C      |           |      |
+----------------+-----------+-----------+------+

Assuming you've launched an interactive zsh login, the shell will check for config files in /etc first, load the contents from those files, then check your home directory.

The zshenv file is loaded first, then your zprofile (Here, we want to place our configs for login shells. This is an alternative to the login file (or .zlogin), which is sourced after the rc). Next is our zshrc, and finally, the zlogin. The zlogout file is executed when you exit the interactive shell.

Notice that on an interactive non-login instance, our zshenv and zshrc files are the only files that are sourced, and the zshenv file is the only file sourced from scripts.

Bonus: Managing Your Dotfiles with GNU Stow

So you've got all these files now, but how do you organize and manage them? If you've consolidated everything to just the .zshrc, then there are no issues with just dropping it in your home directory and leaving it at that, but if you expect your configs to grow and want a way to organize them, keep backups, and use some version control then you can place them all in a git repository and use a symbolic link manager like GNU Stow.

We'll start by taking a look at stow and building out a directory structure that it can use to manage our dotfiles. Create a directory in your $HOME called .dotfiles and create a zsh subdirectory inside it, then move (mv, not cp) the dotfiles we've worked on to that directory, like so:

$ tree -a ~/.dotfiles 
/home/btp/.dotfiles/
└── zsh
    ├── .aliases
    ├── .zshenv
    └── .zshrc

1 directory, 3 files

This .dotfiles directory will be our root directory when using stow, and inside this directory we'll be storing our stow "packages", which we'll be calling stow on to install.

In this example, we'll be creating a zsh package which will install the three config files we've created to the target directory we give to stow.

By default, the target directory is the directory above the stow root directory, which is our home directory in this case. If you want to change the target directory, add the -T /path/to/target flag and argument.

First, let's install this zsh package with stow. Run the following command in your .dotfiles directory.

~/.dotfiles] $ stow --stow zsh

This will call stow on our zsh package, and install our dotfiles in the directory above our .dotfiles directory, which is $HOME. The --stow flag can also be -S. Stow uses symbolic links, and "installs" by creating the symbolic link in the target directory.

This is the same as if you would run ln -s /home/user/.dotfiles/zsh/.zshrc /home/user/ for each of these files.

Now consider the following stow packages:

$ tree -a ~/.dotfiles
/home/btp/.dotfiles
├── alacritty
│   └── .config
│       └── alacritty
│           └── alacritty.toml
└── zsh
    ├── .aliases
    ├── .zshenv
    └── .zshrc

4 directories, 4 files

In this case, we've added a config package for the terminal Alacritty. Stow will check the full path under the package, and mirror it to our target location. When running the stow command on this package, it will add the full config path ~/.config/alacritty/alacritty.toml, which is exactly where we want it.

You can layer your Stow root directory however you want, but when you install packages, you'll need to navigate to the directory that holds the package itself; Stow will not accept a path to a package:

# this will NOT work.
~] $ stow -S .dotfiles/zsh

I keep my .dotfiles in a git repository and hold configs for multiple operating systems there, then navigate to the relevant OS directory for installs, like so.

tree ~/.dotfiles/
└── dots
    ├── linux
    │   ├── alacritty
    │   ├── awesome
    │   ├── helix
    │   ├── nushell
    │   ├── nvim
    │   ├── p10k
    │   ├── powershell
    │   ├── starship
    │   ├── tmux
    │   └── zsh
    ├── macos
    │   ├── alacritty
    │   ├── helix
    │   ├── nushell
    │   ├── nvim
    │   ├── p10k
    │   ├── powershell
    │   ├── starship
    │   ├── tmux
    │   └── zsh
    └── wsl
        ├── helix
        ├── nushell
        ├── p10k
        ├── powershell
        ├── starship
        ├── tmux
        └── zsh

Conclusion

I tried to limit the scope of this article to avoid confusion, and also to avoid a massive post. This topic is very subjective, so take these examples as just that, examples. I've found what works for me when building and managing my config files in a scaleable way, and I hope this has helped you as well. Enjoy!