README.md

Shell Parameter

The ‘$’ character introduces parameter expansion, command substitution, or arithmetic expansion.

Init value

	#Set var2 = $var1 or "defaultval" if $var1 not set or is null
	var2=${var1:-"defaultval"}

	#Set var1 = "defaultvalue" if $var1 not set or is null
	: ${var1:="defaultvalue"}

	#if unset or null var1 prints to stderror var1 is undefined"
	: ${var1:?" is undefined"}

	#if is set var1 prints to stderror var1 is defined"
	echo ${var1:+"is defined"}

Manage Value

Code	Description
${#parameter}	calculate the length
${parameter:offset:length}	Returns the portion of string specified by the offset and length parameters.
${parameter#word}	Remove prefix
${parameter##word}	Remove the longest matching pattern prefix
${parameter%word}	Remove suffix
${parameter%%word}	Remove the longest matching pattern suffix
${parameter/pattern/string}	Replace first match
${parameter//pattern/string}	Replace all match
${parameter^pattern}	Converts lowercase letters matching pattern to uppercase
${parameter^^pattern}	Converts lowercase letters all matching pattern to uppercase
${parameter,pattern}	Converts matching uppercase letters to lowercase
${parameter,,pattern}	Converts all matching uppercase letters to lowercase

HOME