# Bash Parameter Subsitition

| Variable                      | 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,} ${var,pattern}        | Convert first character to lowercase.                        |
| ${var,,} ${var,,pattern}      | Convert all characters to lowercase.                         |
| ${var^} ${var^pattern}        | Convert first character to uppercase.                        |
| ${var^^} ${var^^pattern}      | Convert all character to uppercase.                          |

## References

* [How To Use Bash Parameter Substitution Like A Pro](https://www.cyberciti.biz/tips/bash-shell-parameter-substitution-2.html)