322 lines
8.4 KiB
Markdown
322 lines
8.4 KiB
Markdown
---
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title: Fish shell
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category: CLI
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layout: 2017/sheet
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prism_languages: [fish]
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updated: 2018-01-31
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weight: -1
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---
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### Keys
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| Shortcut | Description |
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| --- | --- |
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| `^A ←`/`^E →` | Move to the line beginning/end |
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| `Alt ←`/`Alt →` | Jump to the previous/next word |
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| `↑`/`↓` | Switch to the previous/next command |
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| `Alt ↑`/`Alt ↓` | Switch to the previous/next arguments |
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| --- | --- |
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| `^U` | Delete to the beginning |
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| `^C` | Cancel the line |
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| --- | --- |
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| `Alt H` | Show the command man page description |
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| `Alt W` | Show the short command description |
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### Sample program
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```fish
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#!/usr/bin/env fish
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echo 'Hello from Fish!'
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```
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### Comments
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```fish
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# my comment
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```
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### Printing text
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```fish
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echo 'Hello from Fish!'
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# or
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printf '%s\n' 'Hello from Fish!'
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```
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Print the string with a trailing `\n`.
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### Reading from stdin
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```fish
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read my_variable
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```
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Reads the string to a variable `my_variable`.
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### Loops
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```fish
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for i in (seq 1 10)
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...
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end
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```
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## Variables
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### Defining and erasing
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```fish
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# Declare the global/local variable:
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set my_variable 'Hello from Fish!'
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i# Remove the variable:
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set --erase my_variable
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```
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### Slicing
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```fish
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echo $my_variable[1..10]
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echo $my_variable[2..]
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echo $my_variable[..-2]
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```
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## Numbers
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### Incrementing and decrementing
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```fish
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set my_variable (math $my_variable + 1)
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set my_variable (math $my_variable - 1)
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```
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### Arithmetic
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```fish
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echo (math 1 + 2)
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```
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| Operator | Performs |
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| --- | --- |
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| `+` | Addition |
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| `-` | Subtraction |
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| `*` | Multiplication |
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| `/` | Division |
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| `%` | Modulo |
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| `^` | Exponentiation |
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## Strings
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### Matching
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Match the string against a regular expresion:
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```fish
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string match --regex --entire 'Fish' 'Hello from Fish!'
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```
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| Pattern | Matches |
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| --- | --- |
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| `x?` | Zero or one `x` chars |
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| `x*` | Any count `x` chars |
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| `x+` | One or more `x` chars |
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| `x{n}` | n times `x` chars |
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| `x{n,m}` | n to m times `x` chars |
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| `x{n,}` | n or more times `x` chars |
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| `[xy]` | `x` or y char |
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| `[^xy]` | not `x` or y char |
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| --- | --- |
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| `\w` | Word character |
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| `\d` | Digit character |
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| `\W` | Not word character |
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| `\D` | Not digit character |
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Perl compatible regular expressions are described here.
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### Replacing
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```fish
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# Replaces the first match
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string replace --regex 'Fish' 'fish' 'Hello from Fish!'
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# Replaces all matches
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string replace --regex --all 'Fish' 'fish' 'Hello from Fish!'
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```
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## Conditionals
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### If/else
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```fish
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if test $my_variable -lt $another_variable
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···
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else if test $my_variable -eq $another_variable
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···
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else
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···
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end
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```
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### Comparisons
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#### Numbers
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| Number operator | Meaning |
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| --- | --- |
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| `-lt` | [L]ess [t]han |
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| `-eq` | [Eq]ual |
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| `-gt` | [G]reater [t]han |
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| `-le` | [L]ess than or [e]qual to |
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| `-ge` | [G]reater than or [e]qual to |
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| `-ne` | [N]ot [E]qual |
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#### Strings
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| String operator | Meaning |
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| --- | --- |
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| `==` | [Eq]ual |
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| `!=` | [N]ot [E]qual |
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#### Files
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| File operator | Meaning |
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| --- | --- |
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| `-f` | [F]ile exists |
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| `-d` | [D]irectory exists |
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| `-r` | File or directory exists and [r]eadable |
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| `-w` | File or directory exists and [w]ritable |
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| `-x` | File or directory exists and e[x]ecutable |
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## Process communication
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### Writing to files
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```fish
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# Overwrite file
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echo 'Hello from Fish!' > my_file
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# Append to file
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echo 'Hello from Fish!' >> my_file
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```
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### Piping
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```fish
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my_command | another_command
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```
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Passes the first command stdout output as an input to a second command.
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### Command substitution
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```fish
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echo (math $my_variable + 1)
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```
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The `(...)` expression is substituted with the output of the command inside it.
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### Process substitution
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```fish
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echo (math $my_variable + 1 | psub)
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```
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The `(... | psub)` expression is substituted with a temporary file with the command's output.
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## Functions
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### Defining and erasing
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```fish
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# Declare the function
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function my_function --description 'My description'
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···
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end
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# Remove the function
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functions --erase my_function
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```
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## Events
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### Emitting
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```fish
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emit my_event
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```
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Emits an event that can be picked up by other functions.
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### Event handling
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```fish
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function my_hook --on-event my_event
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···
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end
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```
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Reacts to the `my_event` event.
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## Abbreviations
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### Defining and erasing
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```fish
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# Declare the abbreviation
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abbr --add grh "git reset --hard HEAD"
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```
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```fish
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# Remove the abbreviation
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abbr --erase grh
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```
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## Completions
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### Defining completions
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```fish
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complete --command mycommand --arguments 'install uninstall'
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complete --command mycommand --short-option 'h' --long-option 'help' --description 'Display help'
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```
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| Option | Description |
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| `--arguments` | Arguments to the command itself or option |
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| `--short-option` | Short option |
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| `--long-option` | Long option |
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| `--no-files` | Don't suggest files |
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| `--force-files` | Suggest files |
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| `--condition` | Display the hint only when a given condition is true |
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| `--description` | Description |
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Declares the completion for a command.
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### Removing completions
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```fish
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complete --command mycommand --erase
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```
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## Useful built-in functions
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| Function | Description |
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| `__fish_seen_argument` | Check whether the specified argument is used |
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| `__fish_seen_subcommand_from` | Check whether the specified subcommand is used |
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| `__fish_use_subcommand` | Check whether any subcommand is used |
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| --- | --- |
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| `__fish_complete_directories` | Complete directories with the specified letters in their name |
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| `__fish_complete_suffix` | Complete files with the specified suffix |
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| --- | --- |
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| `__fish_complete_users` | List all users |
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| `__fish_complete_groups` | List all user groups |
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| `__fish_print_hostnames` | List all host names |
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| `__fish_complete_pids` | List all PIDs |
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| `__fish_print_filesystems` | List all known filesystems |
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| `__fish_print_interfaces` | List all network interfaces |
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