Fish shell

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
---	---
Alt .	Repeat last argument

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 expression:

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