Added introduction.
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Dylan Araps
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# Parameter Expansion
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# Escape Sequences
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## Indirection
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Contrary to popular belief, there's no issue in using raw escape sequences. Using `tput` just abstracts the same ANSI escape sequences. What's worse is that `tput` isn't actually portable, there are a number of different `tput` variants on different Operating Systems each with different commands (*try and run `tput setaf 3` on a FreeBSD system*). The easiest solution ends up being raw ANSI sequences.
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| Parameter | What does it do? |
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| --------- | ---------------- |
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| `${!VAR}` | Access a variable based on the value of `VAR`. See: [link](#assign-and-access-a-variable-using-a-variable)
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| `${!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`. |
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## Text Colors
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**NOTE:** Sequences requiring RGB values only work in True-Color Terminal Emulators.
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| Sequence | What does it do? | Value |
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| -------- | ---------------- | ----- |
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| `\e[38;5;<NUM>m` | Set text foreground color. | `0-255`
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| `\e[48;5;<NUM>m` | Set text background color. | `0-255`
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| `\e[38;2;<R>;<G>;<B>m` | Set text foreground color to RGB color. | `R`, `G`, `B`
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| `\e[48;2;<R>;<G>;<B>m` | Set text background color to RGB color. | `R`, `G`, `B`
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## Text Attributes
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| Sequence | What does it do? |
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| -------- | ---------------- |
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| `\e[m` | Reset text formatting and colors.
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| `\e[1m` | Bold text. |
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| `\e[2m` | Faint text. |
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| `\e[3m` | Italic text. |
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| `\e[4m` | Underline text. |
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| `\e[5m` | Slow blink. |
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| `\e[7m` | Swap foreground and background colors. |
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## Replacement
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## Cursor Movement
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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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| Sequence | What does it do? | Value |
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| -------- | ---------------- | ----- |
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| `\e[<LINE>;<COLUMN>H` | Move cursor to absolute position. | `line`, `column`
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| `\e[H` | Move cursor to home position (`0,0`). |
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| `\e[<NUM>A` | Move cursor up N lines. | `num`
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| `\e[<NUM>B` | Move cursor down N lines. | `num`
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| `\e[<NUM>C` | Move cursor right N columns. | `num`
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| `\e[<NUM>D` | Move cursor left N columns. | `num`
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| `\e[s` | Save cursor position. |
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| `\e[u` | Restore cursor position. |
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## Default Value
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## Erasing Text
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| Parameter | What does it do? |
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| --------- | ---------------- |
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| `${VAR:-STRING}` | If `VAR` is empty or unset, use `STRING` as it's value.
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| `${VAR-STRING}` | If `VAR` is unset, use `STRING` as it's 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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| `${VAR:+STRING}` | If `VAR` isn't empty, use `STRING` as it's value.
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| `${VAR+STRING}` | If `VAR` is set, use `STRING` as it's 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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| Sequence | What does it do? |
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| -------- | ---------------- |
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| `\e[K` | Erase from cursor position to end of line.
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| `\e[1K` | Erase from cursor position to start of line.
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| `\e[2K` | Erase the entire current line.
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| `\e[J` | Erase from the current line to the bottom of the screen.
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| `\e[1J` | Erase from the current line to the top of the screen.
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| `\e[2J` | Clear the screen.
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| `\e[2J\e[H` | Clear the screen and move cursor to `0,0`.
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<!-- CHAPTER END -->
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