71 lines
2.7 KiB
Plaintext
71 lines
2.7 KiB
Plaintext
# PARAMETER EXPANSION
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## Indirection
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| Parameter | What does it do? |
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| --------- | ---------------- |
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| `${!VAR}` | Access a variable based on the value of `VAR`.
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| `${!VAR*}` | Expand to `IFS` separated list of variable names starting with `VAR`. |
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| `${!VAR@}` | Expand to `IFS` separated list of variable names starting with `VAR`. If double-quoted, each variable name expands to a separate word. |
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## Replacement
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| Parameter | What does it do? |
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| --------- | ---------------- |
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| `${VAR#PATTERN}` | Remove shortest match of pattern from start of string. |
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| `${VAR##PATTERN}` | Remove longest match of pattern from start of string. |
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| `${VAR%PATTERN}` | Remove shortest match of pattern from end of string. |
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| `${VAR%%PATTERN}` | Remove longest match of pattern from end of string. |
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| `${VAR/PATTERN/REPLACE}` | Replace first match with string.
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| `${VAR//PATTERN/REPLACE}` | Replace all matches with string.
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| `${VAR/PATTERN}` | Remove first match.
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| `${VAR//PATTERN}` | Remove all matches.
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## Length
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| Parameter | What does it do? |
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| --------- | ---------------- |
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| `${#VAR}` | Length of var in characters.
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| `${#ARR[@]}` | Length of array in elements.
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## Expansion
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| Parameter | What does it do? |
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| --------- | ---------------- |
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| `${VAR:OFFSET}` | Remove first `N` chars from variable.
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| `${VAR:OFFSET:LENGTH}` | Get substring from `N` character to `N` character. <br> (`${VAR:10:10}`: Get sub-string from char `10` to char `20`)
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| `${VAR:: OFFSET}` | Get first `N` chars from variable.
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| `${VAR:: -OFFSET}` | Remove last `N` chars from variable.
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| `${VAR: -OFFSET}` | Get last `N` chars from variable.
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| `${VAR:OFFSET:-OFFSET}` | Cut first `N` chars and last `N` chars. | `bash 4.2+` |
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## Case Modification
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| Parameter | What does it do? | CAVEAT |
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| --------- | ---------------- | ------ |
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| `${VAR^}` | Uppercase first character. | `bash 4+` |
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| `${VAR^^}` | Uppercase all characters. | `bash 4+` |
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| `${VAR,}` | Lowercase first character. | `bash 4+` |
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| `${VAR,,}` | Lowercase all characters. | `bash 4+` |
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| `${VAR~}` | Reverse case of first character. | `bash 4+` |
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| `${VAR~~}` | Reverse case of all characters. | `bash 4+` |
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## Default Value
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| Parameter | What does it do? |
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| --------- | ---------------- |
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| `${VAR:-STRING}` | If `VAR` is empty or unset, use `STRING` as its value.
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| `${VAR-STRING}` | If `VAR` is unset, use `STRING` as its value.
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| `${VAR:=STRING}` | If `VAR` is empty or unset, set the value of `VAR` to `STRING`.
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| `${VAR=STRING}` | If `VAR` is unset, set the value of `VAR` to `STRING`.
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| `${VAR:+STRING}` | If `VAR` is not empty, use `STRING` as its value.
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| `${VAR+STRING}` | If `VAR` is set, use `STRING` as its value.
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| `${VAR:?STRING}` | Display an error if empty or unset.
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| `${VAR?STRING}` | Display an error if unset.
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<!-- CHAPTER END -->
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