Bash Workshop

Installation

Before getting started, you'll want to make sure you have the latest version of Bash installed.

Windows

If you're on Windows, you'll need to install either Git Bash or WSL. If you intend to do more than the basics, it's recommended to install WSL. Git Bash comes with a complete Bash shell, but it's missing much of what you'd expect from a typical unix + bash environment. WSL is a full Linux environment, and will allow you to install any Linux package you might want to use in your bash scripts.

• Git Bash
• WSL

Mac

MacOS comes with a fairly outdated version of Bash (3.2.57, released in 2007). If you're on a Mac, you'll want to install a newer version of Bash. The most common way to do this is to install Homebrew, and then install Bash using Homebrew.

Homebrew is a package manager, much like apt on Ubuntu or the App Store on your phone. It allows you to install and update software from the command line. Since MacOS comes with many command line programs that are either outdated or not compatible with some Linux bash scripts, Homebrew has the added benefit of allowing you to install newer versions of these programs -- not just bash.

• Homebrew
• Installation Guide

Linux

If you're on Linux, you almost certainly already have a recent version of Bash installed. But if you want to make sure, you can run one of the following:

Ubuntu / Debian

sudo apt update
sudo apt install bash

Fedora / CentOS

sudo yum update
sudo yum install bash

Using the run script

This repository comes with a run.sh script that will print out the contents of a file, running each code block inline. This is useful for running the examples in this repository. To use it, simply run:

$ ./run.sh <filename>

Example:

$ ./run.sh examples/foo.sh
examples/foo.sh
#!/bin/bash
#
# This is a demo

> let a=1 b=2 c="a + b"
> echo "a = ${a}
a = 1

> echo "b = ${b}"
b = 2

> echo "c = ${c}"
c = 3

About Bash

Bash is a command line shell. It's a program that runs in your terminal and allows you to run commands. There are actually very few commands that are built into Bash. Most of the commands you run are actually separate programs on your computer. For example, grep is a commonly used program that searches for patterns in files, but it's not part of Bash; it's a program (typically located at /bin/grep) that Bash will run when you type grep.

You can see a list of the built-in features of Bash by running:

man builtins

Environment variables

Bash has a number of environment variables that you can use to customize your shell. You can view all of your environment variables by running env:

$ env
TERM_PROGRAM=Apple_Terminal
SHELL=/bin/bash
TERM=xterm-256color
...

You can also view the value of a single variable by using echo:

$ echo $TERM
xterm-256color

PATH

The PATH variable is a list of directories that Bash will search when you run a command. For example, if you run ls, Bash will search each directory in PATH for a program called ls. If it finds one, it will run that program.

The default value of PATH is typically /usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin. So if you run ls, Bash will search for /usr/local/bin/ls, then /usr/bin/ls, then /bin/ls, and so on. Once it hits a match, it will run that program.

You can add more directories to your PATH by adding them to the end of the variable in one of your startup scripts (see below).

~/.bash_profile

export PATH=$PATH:/usr/local/go/bin

PS1

The PS1 variable is used to customize your prompt. The default value is \h:\W \u\$ , which will display your hostname, current working directory, and username. You can customize this to display whatever you want. For example, if you want to display the current time, you can use \t:

~/.bash_profile

export PS1="\t \u\$ "

Startup script

When you open a new terminal, Bash will run a few startup scripts:

• /etc/profile
• ~/.bash_profile
• ~/.bash_login
• ~/.profile
• ~/.bashrc

The first one is run for all users, and the rest are run for the current user. You can use these scripts to set up your environment, such as adding directories to your PATH variable (see below), setting up your prompt, and generally customizing your shell.

Bash doesn't always run all of these scripts. It depends on how you open your shell. For example, if you open a new terminal window in MacOS, Bash will run /etc/profile, ~/.bash_profile, and ~/.bashrc. But if you open a new terminal tab, it will only run ~/.bashrc. A common pattern to ensure that everything is run is to add the following to your ~/.bash_profile:

~/.bash_profile

if [ -f ~/.bashrc ]; then
    source ~/.bashrc
fi

This ensures that whenever ~/.bash_profile is loaded, it will also load the contents of ~/.bashrc.