The Zsh Shell - Mac Tutorial

History of Zsh Shell with macOS

When Apple released macOS Catalina at WWDC 2019 on October 7, 2019, it was shipped with Zsh shell as the default login shell and interactive shell, replacing the Bash shell which had been the default shell since the Mac OS X Panther that was released in year 2003.

Though Bash is still shipped with all the macOS ever since Catalina till date (macOS Monterey being the latest release), when you open the Terminal app you will see that the prompt as a Percentage (% = Zsh) and not Hash (# = Bash)

If you move from Zsh shell to bash you will see a warning "The default interactive shell is now zsh"

% bash

The default interactive shell is now zsh.
To update your account to use zsh, please run `chsh -s /bin/zsh`.
For more details, please visit https://support.apple.com/kb/HT208050.
bash-3.2$ 

Why Bash was replaced by Zsh Shell in macOS?

To know why, lets go to the GNU page for Bash and look for its releases: https://ftp.gnu.org/gnu/bash/

Now let me see the version of Bash that's shipped with macOS Monterey 12.2,

 % sw_vers
ProductName:	macOS
ProductVersion:	12.2.1
BuildVersion:	21D62

 % bash -version
GNU bash, version 3.2.57(1)-release (arm64-apple-darwin21)
Copyright (C) 2007 Free Software Foundation, Inc.

As you can see that the version for Bash is quite old 3.2 that was released back in the year 2006!, while we have version 4 that was in year 2009 and version 5 in the year 2019.

Why? Though Apple have not provided the reason for it, it is clear if you see the license of Bash v3.2 it is GPL v2 (General Public Licence) where as all Bash versions released after it are GPL v3.

• GNU Free Documentation License Version 2, November 2002
• GNU Free Documentation License Version 3, 29 June 2007

Zsh shell had been getting popular among users and its licensed under MIT-Modern-Varian

What is Zsh?

• Zsh, read as Z shell is a Unix Shell (Bash is a Unix Shell as well)

• Zsh shell is shipped as the default login and interactive shell with Apple macOS since Catalina

• It is an extension of sh (Bourne shell)

• Zsh is incorporated with most of the features from bash, zsh, tcsh and sh shell along with many new features.

• Zsh is also a powerful scripting language.

History of Zsh?

• The first version of Zsh was written by Paul Falstad in the 1990

• The name zsh has been derived from the name of professor Zhong Shao of Yale University.

Zsh Startup Files

Just like bash, Zsh shell has a list of startup files that helps to create the environment you interact with.

1. ~/.zshenv : Zsh Environment File

   The .zshenv file is always sourced, so it is the ideal file to place all your environment variables. The most commonly used $PATH, $JAVA_HOME, $ZDOTDIR environment variables can go in here. All variables that are shared across programs can go in here.

   Example:

   % nano ~/.zshenv

   Adding PATH and other environment variables:

   PATH=$PATH:/opt/homebrew/bin
   PROD_ENV_DIR=/usr/bin/mydir

   Apply changes:

   % source ~/.zshenv

   Testing:

   % echo $PROD_ENV_DIR
   /usr/bin/mydir

2. ~/.zprofile : Zsh Profile File

   .zshprofile file is kind of similar to .zlogin, except that it is source before the .zshrc, you can also use this file as an alternative to .zlogin

   Note: It is recommended that you do not use both .zprofile and .zlogin files together!

3. ~/.zshrc : Zsh Interactive shell configuration file

   .zshrc is the one that is associated with the interactive shell. setopt and unsetopt commands can be used here. The variables that not to shared across programs can be set here. You can also place aliases here.

4. ~/.zlogin : Zsh login File

   As discussed earlier, .zlogin file is similar to .zshenv, this file is read before .zshrc

5. ~/.zlogout: Zsh logout File

   As you must have realised from its name, this file is read at the time of exiting the zsh shell. It will clear and reset the terminal.

Last login: Sat Mar 12 21:36:40 on ttys000
.zshenv Startup file read...
.zshprofile Startup file is raed..
.zshrc Startup file read...
.zlogin Startup file read...
code2care@Code2cares-MacBook-Air ~ % 

How to defile aliases in Zsh Shell?

There are many commands that we use in Terminal often that may have many parameters (optional parameters) or are hard to remember and may take a while to type, alias command can help you to create shortcuts or name such commands with aliases that can help you speed up.

desktop: Most often I save files on my desktop, so whatever directory I am and I want to go to desktop this alias takes me there,

Open ~/.zshrc file and add the below line,

alias desktop='cd /Users/code2care/Desktop'

Apply the changes "source ~/.zshrc", now if you desktop will run as a command,

% desktop
% pwd
/Users/code2care/Desktop

Let's see one more example, if you are used to using cls command on Windows Command Line, you might find it useful to set it as an alias to so you can use either of cls or clear.

alias cls="clear"

Read More: https://code2care.org/zsh/zsh-shell-custom-alias-useful-examples

How to define Functions in Zsh Shell?

You can create your own custom functions in Zsh Shell, lets start with "Hello World" example,

Open .zshrc file and add the below function,

function myZshHelloWorldFunction () {
 echo "Hello World!"
}

Apply changes source ~/.zshrc, now if you type myZshHelloWorldFunction on the prompt you will see "Hello World!" returned on the prompt,

% myZshHelloWorldFunction
Hello World!