Bash Scripting Cheat Sheet

The ability to automate tasks with Bash scripts in Linux is one of the operating system’s most powerful components.

However, due to the sheer amount of scripting components, it can be intimidating for newcomers. Even longtime users may forget something every once in a while and that is why we have created this Bash scripting cheat sheet.

For times like these, it’s very handy to have a compiled list of Bash scripting components that have been sorted by category. That way, it only takes a few moments to reference the list whenever you forget the exact syntax of an operator or conditional statement, etc.

In this tutorial, we’ll present you with a curated list of the most handy things to know for Bash scripting. These are some of the most useful components, but they aren’t easy to remember for everyone. Next time your mind is blanking when writing a Bash script, take a look at the Bash scripting cheat sheet below for some quick help.

In this tutorial you will learn:

  • Bash Scripting Cheat Sheet
Bash Scripting Cheat Sheet
Bash Scripting Cheat Sheet
Software Requirements and Linux Command Line Conventions
Category Requirements, Conventions or Software Version Used
System Any Linux distro
Software Bash shell (installed by default)
Other Privileged access to your Linux system as root or via the sudo command.
Conventions # – requires given linux commands to be executed with root privileges either directly as a root user or by use of sudo command
$ – requires given linux commands to be executed as a regular non-privileged user

Bash Scripting Basics



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Here are some of the most basic things to know about Bash scripting. If you are not sure where to start, this would be a good choice.

Syntax Description
#!/bin/bash Shebang that goes on the first line of every Bash script
#!/usr/bin/env bash Alternative (and better) shebang – using environment variable
# Used to make comments, text that comes after it will not be executed
chmod +x script.sh && ./script.sh Give script executable permissions and execute it
$# Stores the number of arguments passed to the Bash script
$1, $2, $3 Variables that store the values passed as arguments to the Bash script
exit Exit from the Bash script, optionally add an error code
Ctrl + C Keyboard combination to stop Bash script in the middle of execution
$( ) Execute a command inside of a subshell
sleep Pause for a specified number of seconds, minutes, hours, or days

Conditional statements

Conditional statements with if or case allow for us to check if a certain condition is true or not. Depending on the answer, the script can proceed different ways.

Syntax Description
if then fi Test a condition and execute the then clause if it is true
if then else fi Execute the then clause if the condition is true, otherwise execute the else clause
if then elif else fi Test multiple conditions and execute whichever clause is true

For case statements it is best to just see a basic example:

#!/bin/bash

day=$(date +"%a")

case $day in 

  Mon | Tue | Wed | Thu | Fri)
    echo "today is a weekday"
    ;;

  Sat | Sun) 
    echo "today is the weekend"
    ;;

  *)
    echo "date not recognized"
    ;; 
esac

Basic if example script:

#!/bin/bash

if [ $1 -eq $2 ]; then
    echo "they are equal"
else
    echo "they are NOT equal"
fi

Bash Loops

Bash loops allow the script to continue executing a set of instructions as long as a condition continues to evaluate to true.

Syntax Description
for do done Continue to loop for a predetermined number of lines, files, etc
until do done Continue to loop until a certain condition is met
while do done Continue to loop as long as a certain condition is true
break Exit the loop and continue to the next part of the Bash script
continue Exit the current iteration of the loop but continue to run the loop

Read User Input

Prompt the user for information to enter by using read command:

#!/bin/bash

read -p "What is your name? " name

echo "Enjoy this tutorial, $name"

Parse input given as arguments to the Bash script:

#!/bin/bash

if [ $# -ne 2 ]; then
	echo "wrong number of arguments entered. please enter two."
	exit 1
fi

echo You have entered $1 and $2.

Arithmetic Operators




Arithmetic operators in Bash give us the ability to do things like addition, subtraction, multiplication, division, and other basic arithmetic inside of a Bash script.

Syntax Description
+ Addition
- Subtraction
* Multiplication
/ Division
% Modulus
** Raise to a power
((i++)) Increment a variable
((i--)) Decrement a variable

Arithmetic Conditional Operators

Arithmetic conditional operators are usually used on two numbers to determine if a certain condition is true or false.

-lt <
-gt >
-le <=
-ge >=
-eq ==
-ne !=

Note that the operators in the left column will work with single brackets [ ] or double brackets [[ ]], whereas the operators in the right column will work only with double brackets.

String Comparison Operators

We can use string comparison operators to determine if a string is empty or not, and to check if a string is equal, less, or greater in length to another string.

= equal
!= not equal
< less then
> greater then
-n s1 string s1 is not empty
-z s1 string s1 is empty

Bash File Testing Operators

In Bash, we can test to see different characteristics about a file or directory.

-b filename Block special file
-c filename Special character file
-d directoryname Check for directory existence
-e filename Check for file existence
-f filename Check for regular file existence not a directory
-G filename Check if file exists and is owned by effective group ID.
-g filename true if file exists and is set-group-id.
-k filename Sticky bit
-L filename Symbolic link
-O filename True if file exists and is owned by the effective user id.
-r filename Check if file is a readable
-S filename Check if file is socket
-s filename Check if file is nonzero size
-u filename Check if file set-ser-id bit is set
-w filename Check if file is writable
-x filename Check if file is executable


Boolean Operators

Boolean operators include and &&, or || and not equal to !. These operators allow us to test if two or more conditions are true or not.

Syntax Description
&& Logical AND operator
|| Logical OR operator
! NOT equal to operator

Closing Thoughts

Feel free to reference this cheat sheet any time that you need a quick refresher. The goal here is to save you as much time as possible when trying to remember a certain Bash scripting component.



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