Variables

Parameter Expansion

Pattern	What it does	Example	Results
`${var:-default}`	Use default value	`${var:-123}`	`$var` gets `123` if it is unset or empty
`${#var}`	Length of variable's contents
`${var%PATTERN}`	Remove Shortest match from the End	`var=Toronto` `echo ${var%o*}`	`Toront`
`${var%%PATTERN}`	Remove Longest match from the End	`var=Toronto` `echo ${var%%o*}`	`T`
`${var#PATTERN}`	Remove Shortest match from the Beginning	`var=Toronto` `echo ${var#*o}`	`ronto`
`${var##PATTERN}`	Remove Longest match from the Beginning	`var=Toronto` `echo ${var##*t}`	`o`
`${var//PATTERN/STRING}`	Replace all instances of PATTERN with STRING	`password=abc123` `printf "%s\n" "${password//?/*}"`	`******`
`${var:OFFSET:LENGTH}`	Return a Substring of `$var`. First character is at offset 0.	`var=Toronto` `echo ${var:2:3}`	`ron`
`${var^PATTERN}`	Convert First character to Uppercase if it matches PATTERN. If PATTERN is omitted, any character is matched.	`var=toronto` `echo ${var^}`	`Toronto`
`${var^^PATTERN}`	Convert All characters to Uppercase if it matches PATTERN. If PATTERN is omitted, any character is matched.	`var=toronto` `echo ${var^^}` `echo ${var^^[nr]}`	`TORONTO` `toRoNto`
`${var,PATTERN}` `${var,,PATTERN}`	Does for Lowercase what `${var^PATTERN}` and `${var^^PATTERN}` does for Uppercase.	`var=TORONTO` `echo ${var,}` `echo ${var,,[T]}`	`tORONTO` `tORONtO`
`${var~PATTERN}` `${var~~PATTERN}`	Does case inversion	`var=Toronto` `echo ${var~~}`	`tORONTO`

$RANDOM returns a different number between 0 and 32,767 each time it is referenced