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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

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

echo "my function runs"


Declare a variable and export it

declare -x myvar=3

Other commands

 Variable  Description   Variable Description