Check if there is parameter	Code: if [ -n "$1" ] && [ -n "$2" ] # note the quoted test strings then  echo "Strings \"$1\" and \"$2\" are not null." else   echo "Strings \"$1\" and \"$2\" are null." fi alternatively:   Code: if [ $1 ] && [ $2 ] then  echo "Strings \"$1\" and \"$2\" are not null." else   echo "Strings \"$1\" and \"$2\" are null." Fi Pasted from <>
Calc value	$(( $1 + $2 ))
Last command exit code	$? ( 0 normal )
Date string	Datestring=`date "+%d%m%Y"`
File output	Echo
Find out if a folder is mounted	if mount|grep FOLDERNAME ; then    echo "mounted" else    echo "unmounted" fi
Find out if a file exists	if [ -r FILEPATH ]; then    echo "exists" else    echo "not exists" fi
UnHide a folder	chflags nohidden ~/Library
Open with specific tool under terminal	open -a Finder /usr/bin/
Make alias to a folder
:	Python 'pass' equivalence
Replace char in string	#!/bin/ksh x=A_B_C_D # replace _ with a space x=$(echo $x|sed 's/_/ /g') echo $x   Pasted from <>
Replace char by sed	mystr=abc/e echo $mystr | sed "s/\//d/g"   #replace '/' to 'd'
:	What?
mkdir -p	-p creates intermediate directories
var=0 let "var+=1"	Add 1 to $var
read -p "Press Enter to continue"	Pause and enter to continue
array[0]="a" array[1]="b"	Array is zero based
${#array[@]}	Array size/length
select item in "${items[@]}"; do    echo item;    break; done;	Selection with array
dirs=(*/)	Store directories in current folder to array dirs
files=(*.dylib)	Store all files with extension name of .dylib to array files
if [ -n "$var_to_test" ]; then ... fi	Check $var_to_test is not null
string='My string';   if [[ $string == *My* ]] then    echo "It's there!" fi	If you prefer the regex approach: if [[ $string =~ .*My.* ]]   Check if string contains certain elements
:	Colon Historically, Bourne shells did have neither true nor false as builtins. true was instead simply aliased to :, and false to something like let 0. Nowadays, the primary reasons for using : are for needing scripts to be portable to ancient versions of Bourne-derived shells. As a simple example, now-ancient versions of the Korn shell (ksh88) did not have a ! command (for negating the exit code). Thus if you want to portably (across Bourne-derived shells) check for failed execution of a command, you could use: if command; then :; else ... fi Note that if requires a non-empty then clause, and comments do not count as non-empty. As an aside on the insanity that is portable shell scripts: for maximum portability, using : is in fact safer than using true. Modern systems typically have a true binary which will be used as a fall-back, if the shell happens to not have this builtin. But in the worst case, neither builtin nor binary exist, and then attempting to execute true will result in a "command not found" error. This, in turn, typically also leads to an exit code != 0, exactly the opposite of what was intended!