Bash string manipulation cheatsheet.

README.md

Bash string manipulation cheatsheet

Assignment
Assign value to variable if variable is not already set, value is returned. Combine with a : no-op to discard/ignore return value.	${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}
Return string length of variable.	${#variable}
Escaping
Single quotes inside a single quoted string.	echo 'Don'\''t break my escape!'
Indirection
Return value of variable name held in indirect, else value.	indirect="apple" apple="fruit" ${!indirect-value}

Reference

• https://tldp.org/LDP/abs/html/string-manipulation.html
• https://tldp.org/LDP/abs/html/parameter-substitution.html
• https://tldp.org/LDP/abs/html/ivr.html
• Special characters:
  • *: https://www.tldp.org/LDP/abs/html/special-chars.html#ASTERISKREF
  • ?: https://www.tldp.org/LDP/abs/html/special-chars.html#WILDCARDQU
• https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_06_02

BASH Lookup ${! and $[!NAME*} can be powerful, too. You can use it to make indirect references

thanks @nightskyguy - I've actually been needing this for a script recently. Nicely timed. 👍