Bash string manipulation cheatsheet.

BASH magic.md

Bash string manipulation cheatsheet

Removal
Delete shortest match of needle from front of haystack	${haystack#needle}
Delete longest match of needle from front of haystack	${haystack##needle}
Delete shortest match of needle from back of haystack	${haystack%needle}
Delete longest match of needle from back of haystack	${haystack%%needle}
Replacement
Replace first match of needle with replacement from haystack	${haystack/needle/replacement}
Replace all matches of needle with replacement from haystack	${haystack//needle/replacement}
If needle matches front of haystack replace with replacement	${haystack/#needle/replacement}
If needle matches back of haystack replace with replacement	${haystack/%needle/replacement}
Substitution
If variable not set, return value, else variable	${variable-value} ${variable=value}
If variable not set or empty, return value, else variable	${variable:-value} ${variable:=value}
If variable set, return value, else null string	${variable+value}
If variable set and not empty, return value, else null string	${variable:+value}
If variable set, use it, else print err_msg and exit 1	${variable?err_msg}
If variable set and not empty, use it, else print err_msg and exit 1	${variable:?err_msg}
Extraction
Extract length characters from variable starting at position	${variable:position:length}
Extract substring characters from variable starting at position ending at the end of string	${variable:position}
String length of variable	${#variable}
Replacement
First match of Pattern, within var replaced with Replacement.	${var/Pattern/Replacement}
All matches of Pattern, within var replaced with Replacement.	${var//Pattern/Replacement}
If prefix of var matches Pattern, then substitute Replacement for Pattern.	${var/#Pattern/Replacement}
If suffix of var matches Pattern, then substitute Replacement for Pattern.	${var/%Pattern/Replacement}
Indirect reference
Matches names of all previously declared variables beginning with varprefix.	${!varprefix*} ${!varprefix@}

Reference

• http://tldp.org/LDP/abs/html/string-manipulation.html.
• http://tldp.org/LDP/abs/html/parameter-substitution.html.
• http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_06_02.