bash.md

layout	title
../../layouts/CheatSheet.astro	Bash Cheatsheet

Synopsis

Bash is a powerful scripting language that is used by many developers. This cheat sheet is a collection of Bash tips and tricks that will help you write better Bash scripts.

Bash Basics

Command	Description
echo	Print a message to the console
printf	Print a formatted message to the console
cat	Print the contents of a file to the console
pwd	Print the current working directory
cd	Change the current working directory
ls	List the contents of a directory
mkdir	Create a new directory
touch	Create a new file
cp	Copy a file or directory
mv	Move a file or directory
rm	Remove a file or directory
find	Find files or directories
grep	Search for a string in a file
wc	Count the number of lines, words, and characters in a file
sort	Sort the lines in a file
uniq	Remove duplicate lines in a file
head	Print the first 10 lines of a file
tail	Print the last 10 lines of a file
man	Display the manual page for a command
which	Display the location of a command
type	Display the type of a command
alias	Create an alias for a command
history	Display the command history
clear	Clear the console
exit	Exit the console

Variables

Command	Description
var="value"	Assign a value to a variable
echo $var	Print the value of a variable
echo ${var}	Print the value of a variable
echo "$var"	Print the value of a variable
echo "${var}"	Print the value of a variable
echo '$var'	Print the literal value of a variable
echo '${var}'	Print the literal value of a variable
echo "${var:-default}"	Print the value of a variable or a default value if the variable is not set
echo "${var:=default}"	Assign a default value to a variable if the variable is not set
echo "${var:?error}"	Print an error message if the variable is not set
echo "${var:+value}"	Print a value if the variable is set
echo "${var:offset}"	Print a substring of a variable

Functions

Command	Description
function_name() { ... }	Define a function
function_name() { echo "Hello World"; }	Define a function
function_name() { echo "Hello $1"; }	Define a function with parameters
function_name() { echo "Hello $@"; }	Define a function with parameters

Arrays

Command	Description
array=(value1 value2 value3)	Define an array
echo ${array[0]}	Print the value of an array element
echo ${array[@]}	Print the values of an array
echo ${#array[@]}	Print the number of elements in an array
echo ${#array[0]}	Print the length of an array element
array[0]="value"	Assign a value to an array element
array+=(value)	Append a value to an array
unset array[0]	Remove an array element
unset array	Remove an array

Conditionals

Command	Description
if [ condition ]; then ... fi	If statement
if [ condition ]; then ... else ... fi	If/else statement
if [ condition1 ]; then ... elif [ condition2 ]; then ... else ... fi	If/elif/else statement
case value in pattern1) ... ;; pattern2) ... ;; esac	Case statement
case value in pattern1) ... ;; pattern2) ... ;; *) ... ;; esac	Case statement with a default case

Loops

Command	Description
for var in value1 value2 value3; do ... done	For loop
for var in $(command); do ... done	For loop
for (( i=0; i<10; i++ )); do ... done	For loop
while [ condition ]; do ... done	While loop
until [ condition ]; do ... done	Until loop

Input/Output

Command	Description
read var	Read input from the console
read -p "Enter a value: " var	Read input from the console with a prompt
read -a array	Read input from the console into an array
read -d	Read input from the console until a delimiter is found
read -s	Read input from the console without echoing the input
read -n	Read a specified number of characters from the console
read -t	Read input from the console with a timeout
echo "Hello World" > file.txt	Redirect output to a file
echo "Hello World" >> file.txt	Append output to a file
echo "Hello World" 2> file.txt	Redirect error output to a file

Debugging

Command	Description
set -x	Enable debugging
set +x	Disable debugging
set -v	Print shell input lines as they are read
set +v	Do not print shell input lines as they are read
set -n	Read commands but do not execute them
set +n	Execute commands read from the command line

Miscellaneous

Command	Description
echo "Hello World"	Print a string
echo -n "Hello World"	Print a string without a newline
echo -e "Hello\tWorld"	Print a string with escaped characters

Bash Advanced

Bash Builtins

Command	Description
.	Execute a script in the current shell
source	Execute a script in the current shell
:	Do nothing
true	Do nothing
false	Do nothing
break	Exit a loop
continue	Skip to the next iteration of a loop
return	Exit a function
exit	Exit the shell
set	Set shell options
unset	Unset shell options
export	Export a variable
readonly	Make a variable read-only
declare	Declare a variable
typeset	Declare a variable
local	Declare a local variable
eval	Evaluate a string as a command
exec	Execute a command
shift	Shift positional parameters
wait	Wait for a background process to complete
pwd	Print the current working directory
cd	Change the current working directory
pushd	Push the current working directory onto the directory stack

Bash Options

Command	Description
set -o	List shell options
set -o noclobber	Do not overwrite existing files
set -o errexit	Exit on error
set -o errtrace	Exit on error in a function
set -o nounset	Exit on unset variable
set -o pipefail	Exit on pipe failure
set -o xtrace	Print commands and their arguments as they are executed

Bash Aliases

Command	Description
alias	List aliases
alias name="command"	Create an alias
unalias	Remove an alias

Bash Functions

Command	Description
function name { ... }	Define a function
name() { ... }	Define a function
declare -f	List functions
declare -f name	List a function

Bash Arrays

Command	Description
array=(value1 value2 value3)	Create an array
array[0]="value"	Assign a value to an array element
array+=(value)	Append a value to an array
unset array[0]	Remove an array element
unset array	Remove an array
declare -a	List arrays
declare -a array	List an array
declare -p	List variables
declare -p array	List a variable

Bash Conditionals

| Command | Description | | -------------------------------- | ------------ | -------------- | ------------ | | [[ condition ]] | If statement | | [[ condition1 && condition2 ]] | If statement | | [[ condition1 | | condition2 ]] | If statement | | [[ ! condition ]] | If statement | | [[ value1 == value2 ]] | If statement | | [[ value1 != value2 ]] | If statement | | [[ value1 < value2 ]] | If statement | | [[ value1 > value2 ]] | If statement |

Bash Loops

Command	Description
for var in "${array[@]}"; do ... done	For loop
for (( i=0; i<10; i++ )); do ... done	For loop
while [[ condition ]]; do ... done	While loop
until [[ condition ]]; do ... done	Until loop
select var in "${array[@]}"; do ... done	Select loop

Bash Input/Output

Command	Description
read -p "Enter a value: " value	Read input from the console
read -p "Enter a value: " -s value	Read input from the console without echoing the input
read -p "Enter a value: " -n 5 value	Read a specified number of characters from the console

Bash Arguments

Command	Description
$#	Specifies number of arguments
$*	Specifies all positional arguments as a single word
$@	Specifies all positional arguments as separate words
$1	Specifies first argument passed
$_	Specifies last argument of the previous command