# The Only Bash Scripting Cheat Sheet That You Will Ever Need

Introduction
------------

No matter if you are a DevOps/SysOps engineer, developer, or just a Linux enthusiast, you can use Bash scripts to combine different Linux commands and automate boring and repetitive daily tasks, so that you can focus on more productive and fun things.

Here you can find the completed Bash Scripting cheat sheet 👇

Bash Script Header (Shebang)
----------------------------

Option 1:

    #!/bin/bash
    

Option 2:

    #!/usr/bin/env bash
    

Variables
---------

    #!/bin/bash
    name="DevDojo"
    echo "Hi there $name"
    

User Input
----------

    #!/bin/bash
    
    echo "What is your name?"
    read name
    
    echo "Hi there $name"
    echo "Welcome to DevDojo!"
    

Comments
--------

To do that in bash you need to add the # symbol at the beginning of the line. Comments will never be rendered on the screen.

    # This is a comment and will not be rendered on the screen
    

Arguments
---------

    #!/bin/bash
    
    echo "Argument one is $1"
    echo "Argument two is $2"
    echo "Argument three is $3"
    

Then run the file and pass 3 arguments:

    bash ./arguments.sh dog cat bird
    

Arrays
------

    my_array=("value 1" "value 2" "value 3" "value 4")
    
    # Access a single element, this would output: value 2
    echo ${my_array[1]}
    
    # This would return the last element: value 4
    echo ${my_array[-1]}
    
    # This would output the total number of elements in the array, in our case, it is 4:
    echo "${#my_array[@]}"
    
    # This would output all of the elements of the array:
    printf '%s\n' "${my_array[@]}"
    

Conditional Expressions
-----------------------

### File expressions

    ## True if file exists.
    [[ -a ${file} ]]
    
    ## True if file exists and is a block special file.
    [[ -b ${file} ]]
    
    ## True if file exists and is a character special file.
    [[ -c ${file} ]]
    
    ## True if file exists and is a directory.
    [[ -d ${file} ]]
    
    ## True if file exists.
    [[ -e ${file} ]]
    
    ## True if file exists and is a regular file.
    [[ -f ${file} ]]
    
    ## True if file exists and is a symbolic link.
    [[ -h ${file} ]]
    
    ## True if file exists and is readable.
    [[ -r ${file} ]]
    
    ## True if file exists and has a size greater than zero.
    [[ -s ${file} ]]
    
    ## True if file exists and is writable.
    [[ -w ${file} ]]
    
    ## True if file exists and is executable.
    [[ -x ${file} ]]
    
    ## True if file exists and is a symbolic link.
    [[ -L ${file} ]]
    

### String expressions

    # True if the shell variable varname is set (has been assigned a value).
    [[ -v ${varname} ]]
    
    # True if the length of the string is zero.
    [[ -z ${string} ]]
    
    # True if the length of the string is non-zero.
    [[ -n ${string} ]]
    
    # True if the strings are equal. = should be used with the test command for POSIX conformance. When used with the [[ command, this performs pattern matching as described above (Compound Commands)
    [[ ${string1} == ${string2} ]]
    
    # True if the strings are not equal.
    [[ ${string1} != ${string2} ]]
    
    # True if string1 sorts before string2 lexicographically.
    [[ ${string1} < ${string2} ]]
    
    # True if string1 sorts after string2 lexicographically.
    [[ ${string1} > ${string2} ]]
    

### Arithmetic operators

    # Returns true if the numbers are equal
    [[ ${arg1} -eq ${arg2} ]]
    
    # Returns true if the numbers are not equal
    [[ ${arg1} -ne ${arg2} ]]
    
    # Returns true if arg1 is less than arg2
    [[ ${arg1} -lt ${arg2} ]]
    
    # Returns true if arg1 is less than or equal arg2
    [[ ${arg1} -le ${arg2} ]]
    
    # Returns true if arg1 is greater than arg2
    [[ ${arg1} -gt ${arg2} ]]
    
    # Returns true if arg1 is greater than or equal arg2
    [[ ${arg1} -ge ${arg2} ]]
    
    # As with other programming languages you can use AND & OR conditions:
    [[ test_case_1 ]] && [[ test_case_2 ]] # And
    [[ test_case_1 ]] || [[ test_case_2 ]] # Or
    

Conditionals
------------

    #!/bin/bash
    
    # Bash if statement example
    
    read -p "What is your name? " name
    
    if [[ -z ${name} ]]
    then
        echo "Please enter your name!"
    else
        echo "Hi there ${name}"
    fi
    

Loops
-----

### For loops

    #!/bin/bash
    
    users="devdojo, bobby, tony"
    
    for user in ${users}
    do
        echo "${user}"
    done
    

### While loops

    #!/bin/bash
    
    counter=1
    while [[ $counter -le 10 ]]
    do
        echo $counter
        ((counter++))
    done
    

### Until Loops

    #!/bin/bash
    
    count=1
    until [ $count -gt 10 ]
    do
        echo $count
        ((count++))
    done
    

Functions
---------

    function function_name() {
        your_commands
    }
    

Example

    #!/bin/bash
    
    function hello(){
        echo "Hello World Function!"
    }
    
    hello
    

Conclusion
----------

For a more in-depth explanations check out this online guide here:

[Bash Scripting Hands-on Guide](https://devdojo.com/guide/bash/bash-conditional-expressions)

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If you want to learn more about Bash Scripting check out this free eBook here:

[💡 Introduction to Bash Scripting](https://github.com/bobbyiliev/introduction-to-bash-scripting)

If you prefer video content, you could take a look at this mini video crash course here:

[Introduction to Bash Scripting Mini Video Crash Course](https://www.youtube.com/playlist?list=PLY7SzAmnEqp78tsHh1kK0gOx_f-uwQZAT)