# Bash # Bash Cheat Sheet #### BASH stands for Bourne-Again SHell each BASH script should start with the shebang : \#!/bin/bash #### Comparison operators

Operator	Description	Operator	Description
-eq	Is equal to	-n	Is not null
-ne	Is not equal to	-z	Is null
-gt	Is greater than	-r	file exists and is readable by the user
-ge	Is greater than or equal to	-e	file exists
-lt	Is less then	-f	file is a regular file (not directory or other special type)
-le	Is less than or equal to	-s	file size is greater then 0
==	is equal to	-x	file is executable by the user
!=	is not equal to	-w	file is writable by the user
<	Is less than	!	negates the operator
<=	Is less than or equal to
>	Is greater then
>=	Is greater than or equal to

#### Variables for script arguments

Variable	Description	Variable	Description
$1 ... $n	Argument number	$#	Number of arguments
$0	Name of the file	$?	Return value (0 = ok, > 0 = error)
$\*	List of arguments

#### Built in variables

Variable	Description	Variable	Description
$BASH	path to the bash binaries	$BASH\_VERSION	version of bash
$BASH\_ENV	bash environment (used within the scripts)	$BASH\_VERSINFO	more version details
$$	process id of the current script	$PATH	path variable
$EDITOR	default editor	$UID	users id
$EUID	effective user id	$FUNCNAME	name of the current function (executed from within the function)
$GROUPS	groups to which the current user belongs	$HOME	home directory of the current user
$HOSTTYPE	system type	$MACHTYPE	machine type
$LINENO	line number	$PWD	print working directory
$OLDPWD	old print working directory	$OSTYPE	operating system type
$REPLY	default answer for a "read" command without explicit variable declaration	$SECONDS	the time the script has run until this point
$RANDOM	Generate a random number between 0 and 32767

##### Declare and a few howtos **Declare a variable as read only** ``` declare -r my_read_only_variable=5 ``` **Declare a variable as an integer** ``` declare -i my_integer_variable=5 ``` **Declare a variable as an array** ``` declare -a myvar=(1 2 3 4 5) ``` **Declare a function and then run it** ``` declare -f myFunction myFunction(){ echo "my function runs" } myFunction ``` **Declare a variable and export it** ``` declare -x myvar=3 ``` #### Other commands

Variable	Description	Variable	Description

Variable	Description	Variable	Description