Fish shell cheatsheet

Keys

Shortcut	Description
`^A ←`/`^E →`	Move to the line beginning/end
`Alt ←`/`Alt →`	Jump to the previous/next word
`↑`/`↓`	Switch to the previous/next command
`Alt ↑`/`Alt ↓`	Switch to the previous/next arguments
`^U`	Delete to the beginning
`^C`	Cancel the line
`Alt H`	Show the command man page description
`Alt W`	Show the short command description

Sample program

#!/usr/bin/env fish

echo 'Hello from Fish!'

Comments

# my comment

Printing text

echo 'Hello from Fish!'
# or
printf '%s\n' 'Hello from Fish!'

Print the string with a trailing \n.

Reading from stdin

read my_variable

Reads the string to a variable my_variable.

Loops

for i in (seq 1 10)
  ...
end

Variables

Defining and erasing

# Declare the global/local variable:
set my_variable 'Hello from Fish!'

i# Remove the variable:
set --erase my_variable

Slicing

echo $my_variable[1..10]
echo $my_variable[2..]
echo $my_variable[..-2]

Numbers

Incrementing and decrementing

set my_variable (math $my_variable + 1)
set my_variable (math $my_variable - 1)

Arithmetic

echo (math 1 + 2)

Operator	Performs
`+`	Addition
`-`	Subtraction
`*`	Multiplication
`/`	Division
`%`	Modulo
`^`	Exponentiation

Strings

Matching

Match the string against a regular expresion:

string match --regex --entire 'Fish' 'Hello from Fish!'

Pattern	Matches
`x?`	Zero or one `x` chars
`x*`	Any count `x` chars
`x+`	One or more `x` chars
`x{n}`	n times `x` chars
`x{n,m}`	n to m times `x` chars
`x{n,}`	n or more times `x` chars
`[xy]`	`x` or y char
`[^xy]`	not `x` or y char
`\w`	Word character
`\d`	Digit character
`\W`	Not word character
`\D`	Not digit character

Perl compatible regular expressions are described here.

Replacing

# Replaces the first match
string replace --regex 'Fish' 'fish' 'Hello from Fish!'

# Replaces all matches
string replace --regex --all 'Fish' 'fish' 'Hello from Fish!'

Conditionals

If/else

if test $my_variable -lt $another_variable
  ···
else if test $my_variable -eq $another_variable
  ···
else
  ···
end

Comparisons

Numbers

Number operator	Meaning
`-lt`	[L]ess [t]han
`-eq`	[Eq]ual
`-gt`	[G]reater [t]han
`-le`	[L]ess than or [e]qual to
`-ge`	[G]reater than or [e]qual to
`-ne`	[N]ot [E]qual

Strings

String operator	Meaning
`==`	[Eq]ual
`!=`	[N]ot [E]qual

Files

File operator	Meaning
`-f`	[F]ile exists
`-d`	[D]irectory exists
`-r`	File or directory exists and [r]eadable
`-w`	File or directory exists and [w]ritable
`-x`	File or directory exists and e[x]ecutable

Process communication

Writing to files

# Overwrite file
echo 'Hello from Fish!' > my_file

# Append to file
echo 'Hello from Fish!' >> my_file

Piping

my_command | another_command

Passes the first command stdout output as an input to a second command.

Command substitution

echo (math $my_variable + 1)

The (...) expression is substituted with the output of the command inside it.

Process substitution

echo (math $my_variable + 1 | psub)

The (... | psub) expression is substituted with a temporary file with the command’s output.

Functions

Defining and erasing

# Declare the function
function my_function --description 'My description'
  ···
end

# Remove the function
functions --erase my_function

Events

Emitting

emit my_event

Emits an event that can be picked up by other functions.

Event handling

function my_hook --on-event my_event
  ···
end

Reacts to the my_event event.

Abbreviations

Defining and erasing

# Declare the abbreviation
abbr --add grh "git reset --hard HEAD"

# Remove the abbreviation
abbr --erase grh

Completions

Defining completions

complete --command mycommand --arguments 'install uninstall'
complete --command mycommand --short-option 'h' --long-option 'help' --description 'Display help'

Option	Description
`--arguments`	Arguments to the command itself or option
`--short-option`	Short option
`--long-option`	Long option
`--no-files`	Don’t suggest files
`--force-files`	Suggest files
`--condition`	Display the hint only when a given condition is true
`--description`	Description

Declares the completion for a command.

Removing completions

complete --command mycommand --erase

Useful built-in functions

Function	Description
`__fish_seen_argument`	Check whether the specified argument is used
`__fish_seen_subcommand_from`	Check whether the specified subcommand is used
`__fish_use_subcommand`	Check whether any subcommand is used
`__fish_complete_directories`	Complete directories with the specified letters in their name
`__fish_complete_suffix`	Complete files with the specified suffix
`__fish_complete_users`	List all users
`__fish_complete_groups`	List all user groups
`__fish_print_hostnames`	List all host names
`__fish_complete_pids`	List all PIDs
`__fish_print_filesystems`	List all known filesystems
`__fish_print_interfaces`	List all network interfaces