BASH SUBSTIUTION OPRATOR

operator	example	rresult
#	${var#pattern}	delete the shortest match of pattern from the front and return the test.
##	${var##parttern}	delete the longgest match of the pettern from front of the var and return the rest
%	${var%pattern}	delete the shortest match of pattern from the end of var, return the rest
%%	${var%%pattern}	delete the longgest march of pattern from the end of var return the rest
/	${var/pattern/string}	replace the longest match of pattern with string, replace only the first mattch
//	${var//pattern/str}	replace the lonnest match of pattern with str, replace all matches

BASH SUBSTITUTION OPERATOR

operator	example	result
:-	${var:-word]	if var exists and nonone, return its value, otherwise return word. var is not changed
:=	${var:=word}	if var exists and nonone.then return the var, otherwise assign the word to var, return new value
:+	${var:+owrd}	if var exists and nonone,return word, else return null
:?	${var:?message}	if var exists and nonone, then return value, else rethrn thr message"basg2:$var:$message" and abort the current command
:n	${var:offset[:length]}	return the length of the substring from the offset. If length iis not, then return the last part string.