Bash string manipulation cheatsheet.

README.md

Bash string manipulation cheatsheet

Assignment
Assign value to variable if variable is not already set. Value will be returned. Couple with : no-op if return value is to be discarded.	${variable="value"} : ${variable="value"}
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}
If variable not set or empty, return value, else variable	${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}
Extraction
Extract length characters from variable starting at position	${variable:position:length}
String length of variable	${#variable}

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.