Lately I have been catching myself looking up bash variable operations too often. This is something I want to keep in the back of my head.
The Bash Beginners Guide gives a good overview on Operations on variables.
TL;DR
| Operation | Description |
|---|---|
${#STR} | Length of the value of $STR |
${STR:-test} | Default $STR to “test” |
[ -z "${INT:-}" ] && INT=80 | Default $INT to value 80 |
${STR:OFFSET} | Keep everything after OFFSET |
${STR:OFFSET:LENGTH} | Keep LENGTH characters after OFFSET |
${STR/PATTERN/STRING} | Replace first occurence of STRING |
${STR//PATTERN/STRING} | Replace all occurences of STRING |
${VAR#WORD} | Remove first occurence of WORD |
${VAR##WORD} | Remove all occurences of WORD |
${VAR#PATTERN} | Remove shortest match of PATTERN |
${VAR##PATTERN} | Remove longest match of PATTERN |
${VAR%WORD} | Keep first occurence of WORD |
${VAR%%WORD} | Keep all occurences of WORD |
${VAR%PATTERN} | Keep shortest match of PATTERN |
${VAR%%PATTERN} | Keep longest match of PATTERN |
Usual Suspects
| Operation | Description | Effectively |
|---|---|---|
${VAR##*/} | Remove path until filename | Keep filename |
${VAR%/*} | Keep the path without filename | Keep dirname |