Lugnuts // Intro to Bash Scripting

Hands-on lessons to go with the Intro to Bash Scripting talk. You don't need any experience. If you can type, you can do this.

What is this?

A bash script is a text file full of commands. When you run it, the computer does those commands one at a time, top to bottom. People use scripts so they don't have to type the same commands over and over: backing up files, setting up computers, checking on servers, and more.

Each lesson is a script you can run and read. The # lines inside each file explain what every part does.

Step 1: Open a terminal

Your computer	How to open a terminal
Linux	Press Ctrl + Alt + T, or search your apps for "Terminal"
Mac	Press Cmd + Space, type Terminal, press Enter
Windows	Install WSL (search "install WSL" on Microsoft's site), then open "Ubuntu" from the Start menu

You'll see a line ending in $ or %. That's the prompt: the terminal waiting for you to type something.

Step 2: Go to the lessons folder

Copy this whole folder onto your computer (for example, into your home folder). Then type cd followed by the folder's location and press Enter. For example:

cd ~/lugnuts_bash_scripting/lessons

Type ls and press Enter. You should see the lesson files listed.

Tip: type the first few letters of a folder or file name and press Tab. The terminal will finish the name for you.

Step 3: Run your first lesson

bash 01_hello_world.sh

You should see Hello, World! and a few facts about your computer. You just ran a script!

Step 4: Read it, change it, run it again

Open the lesson in a text editor to see how it works. nano is the easiest one to start with:

nano 01_hello_world.sh

Inside nano: use the arrow keys to move around and type to make changes. Press Ctrl + O and then Enter to save, and Ctrl + X to quit.

Each lesson ends with a TRY IT YOURSELF section. Don't skip it. Changing things and breaking them is how this stuff sticks.

The lessons

Do them in order. Each one builds on the last.

#	File	You'll learn
1	lessons/01_hello_world.sh	What a script is, the #!/bin/bash line, comments, echo
2	lessons/02_essential_commands.sh	ls, cd, pwd, mkdir, touch, cat, cp, mv, rm, grep, man
3	lessons/03_variables.sh	Saving values, built-in variables, asking the user questions
4	lessons/04_conditionals.sh	Making decisions with if / else
5	lessons/05_loops.sh	Repeating things with for, while, and until
6	lessons/06_functions.sh	Making your own mini commands

Projects: real scripts you can actually use

Once you've finished the lessons, these put it all together. Run them from the projects folder.

File	What it does	Try it
projects/sysinfo.sh	Prints a health report for your computer	bash sysinfo.sh
projects/backup.sh	Backs up any folder into a dated, compressed file	bash backup.sh ~/Documents

Word list

Word	What it means
terminal	The window you type commands into
shell / bash	The program inside the terminal that understands your commands. Bash is the most common one
command	An instruction, like ls or echo
option	A setting that changes a command, usually starting with -. In ls -l, the -l is an option
argument	Extra info you give a command. In cd Documents, Documents is the argument
directory	Another word for folder
path	Where a file lives, like /home/alice/notes.txt
~	Shortcut for your home folder
.	"This folder"
..	"The folder above this one"
./	"Run the file in this folder", like ./myscript.sh
#!/bin/bash	The "shebang": the first line of a script, saying which program runs it
sudo	"Run this as the administrator." Only use it when you have to, and always read the command first

Common mistakes (everyone makes these!)

What you see	What's wrong	Fix
No such file or directory	You're in the wrong folder, or there's a typo in the name	Run pwd to see where you are and ls to see what's there
Permission denied when running ./script.sh	The file isn't allowed to run yet	Run chmod +x script.sh once, or use bash script.sh instead
command not found after name = "value"	Spaces around the =	Write it as name="value" with no spaces
[: missing ']'	No space inside the brackets	Write [ "$a" = "b" ] with spaces next to [ and ]
Script seems frozen	It's waiting for you to type something, or it's stuck in a loop	Type an answer and press Enter, or press Ctrl + C to stop it

Getting help

• man ls opens the manual for any command (here, ls). Press q to quit.
• explainshell.com: paste a command and it explains each piece.
• shellcheck.net: paste your script and it points out mistakes.
• Ask people around you for help!

Already know bash or you're done, it's time for OverTheWire Bandit

OverTheWire Bandit is a free game played entirely in the terminal. Each level teaches a new command, and it's how a lot of us learned. Start at Level 0 and come to a meetup to work through it together!