Fred
Monday, June 8, 2020 | 1 minute
Bash Variables Substitutions
This table summarizes Bash parameter expansions, providing a quick reference for manipulating shell variables. It covers operations like default value assignment, substring extraction, pattern removal, case conversion, and string length calculation.
| Parameter Expansion | Description |
|---|---|
${parameter:-defaultValue} | Get default shell variables value |
${parameter:=defaultValue} | Set default shell variables value |
${parameter:?"Error Message"} | Display an error message if parameter is not set |
${#var} | Find the length of the string |
${var%pattern} | Remove from shortest rear (end) pattern |
${var%%pattern} | Remove from longest rear (end) pattern |
${var:num1:num2} | Substring |
${var#pattern} | Remove from shortest front pattern |
${var##pattern} | Remove from longest front pattern |
${var/pattern/string} | Find and replace (only replace first occurrence) |
${var//pattern/string} | Find and replace all occurrences |
${!prefix*} | Expands to the names of variables whose names begin with prefix. |
${var,} | Convert first character to lowercase. |
${var,pattern} | Convert first character to lowercase. |
${var,,} | Convert all characters to lowercase. |
${var,,pattern} | Convert all characters to lowercase. |
${var^} | Convert first character to uppercase. |
${var^pattern} | Convert first character to uppercase. |
${var^^} | Convert all character to uppercase. |
${var^^pattern} | Convert all character to uppercase. |