Bash Basics Cheat Sheet (DRAFT) by [deleted]

Variable	Meaning
$0	Name of the current script
$1 - $9	Positional parameters #1 - #9
${10}	Positional parameters #10
$#	Number of positional parameters
"­$*"	All the positional parameters as one single word
"­$@"	All the positional parameters as separated strings
${#*} or ${#@}	Number of command line parameters passed to script
$?	Return value
$$	Process ID of the script
$-	Flags passed to Script
$_	Last argument of previous command
$!	Process ID of Last Job in background

Expression	Meaning
if [ ... ] then --- fi	If [ value ] is true, then do ---
if [[ ... ]] then --- fi	If [[ value ]] is true, then do --- (extended condition
while [ ... ] do --- done	while [ value ] is true, do ---
(( ... ))	Arithmetic operation

Arithe­metic Operator	Meaning
>	Greater than
>=	Greater than or equal to
<	Less than
<=	Less than or equal to

Operator	Meaning
-e	File Exists
-f	file is a regular file
-d	file is a directory
-h or -L	file is a symbolic link
-b	File is a block device
-N	File modified since it was last read
-O	You own the file
-G	Group ID of the file is the same as yours
!	Reverse the sense of the above tests
-s	Size of the file is not 0
-r	File has read permission
-w	File has write permission
-x	File has execute permission
-nt	Is newer than
-ot	Is older than