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fish tutorial

Why fish?

fish is a fully-equipped command line shell (like bash or zsh) that is smart and user-friendly. fish supports powerful features like syntax highlighting, autosuggestions, and tab completions that just work, with nothing to learn or configure.

If you want to make your command line more productive, more useful, and more fun, without learning a bunch of arcane syntax and configuration options, then fish might be just what you're looking for!

Learning fish

This tutorial assumes a basic understanding of command line shells and Unix commands, and that you have a working copy of fish.

If you have a strong understanding of other shells, and want to know what fish does differently, search for the magic phrase unlike other shells, which is used to call out important differences.

When you start fish, you should see this: 

Welcome to fish, the friendly interactive shell
Type help for instructions on how to use fish
you@hostname ~>

fish comes with a default prompt that shows your username, hostname, and working directory. You'll see how to change your prompt further down. From now on, we'll pretend your prompt is just a '>' to save space.

Running Commands

fish runs commands like other shells: you type a command, followed by its arguments. Spaces are separators: 

> echo hello world
hello world
You can include a literal space in an argument with a backslash, or by using single or double quotes: 
> mkdir My\ Files
> cp ~/Some\ File 'My Files'
> ls "My Files"
Some File
Commands can be chained with semicolons.

Getting Help

fish has excellent help and man pages. Run help to open help in a web browser, and man to open it in a man page. You can also ask for help with a specific command, for example, help set to open in a web browser, or man set to see it in the terminal. 
> man set
set - handle environment variables
  Synopsis...

Syntax Highlighting

You'll quickly notice that fish performs syntax highlighting as you type. Invalid commands are colored red by default: 
> /bin/mkd
A command may be invalid because it does not exist, or refers to a file that you cannot execute. When the command becomes valid, it is shown in a different color: 
> /bin/mkdir
fish will underline valid file paths as you type them: 
> cat ~/somefi

This tells you that there exists a file that starts with 'somefi', which is useful feedback as you type.

These colors, and many more, can be changed by running fish_config, or by modifying variables directly.

Wildcards

fish supports the familiar wildcard *. To list all JPEG files: 
> ls *.jpg
lena.jpg
meena.jpg
santa maria.jpg

You can include multiple wildcards: 

> ls l*.p*
lena.png
lesson.pdf

Especially powerful is the recursive wildcard ** which searches directories recursively: 

> ls /var/**.log
/var/log/system.log
/var/run/sntp.log

If that directory traversal is taking a long time, you can Control-C out of it.

Pipes and Redirections

You can pipe between commands with the usual vertical bar: 

> echo hello world | wc
           1       2      12

stdin and stdout can be redirected via the familiar < and >. Unlike other shells, stderr is redirected with a caret ^ 

> grep fish < /etc/shells > ~/output.txt ^ ~/errors.txt

Autosuggestions

fish suggests commands as you type, and shows the suggestion to the right of the cursor, in gray. For example: 
> /bin/hostname
It knows about paths and options: 
> grep --ignore-case
And history too. Type a command once, and you can re-summon it by just typing a few letters: 
> rsync -avze ssh . myname@somelonghost.com:/some/long/path/doo/dee/doo/dee/doo
To accept the autosuggestion, hit right arrow or Control-F. To accept a single word of the autosuggestion, hit Alt+right arrow. If the autosuggestion is not what you want, just ignore it.

Tab Completions

fish comes with a rich set of tab completions, that work "out of the box."

Press tab, and fish will attempt to complete the command, argument, or path: 

> /pri<tab> → /private/

If there's more than one possibility, it will list them: 

> ~/stuff/s<tab>
~/stuff/script.sh  (Executable, 4.8kB)  ~/stuff/sources/  (Directory)

Hit tab again to cycle through the possibilities.

fish can also complete many commands, like git branches: 

> git merge pr<tab> → git merge prompt_designer
> git checkout b<tab>
builtin_list_io_merge  (Branch)  builtin_set_color  (Branch)  busted_events  (Tag)
Try hitting tab and see what fish can do!

Variables

Like other shells, a dollar sign performs variable substitution: 

> echo My home directory is $HOME
My home directory is /home/tutorial
Variable substitution also occurs in double quotes, but not single quotes: 
> echo "My current directory is $PWD"
My current directory is /home/tutorial
> echo 'My current directory is $PWD'
My current directory is $PWD
Unlike other shells, fish has no dedicated syntax for setting variables. Instead it has an ordinary command: set, which takes a variable name, and then its value. 
> set name 'Mister Noodle'
> echo $name
Mister Noodle

(Notice the quotes: without them, Mister and Noodle would have been separate arguments, and $name would have been made into a list of two elements.)

Unlike other shells, variables are not further split after substitution: 

> mkdir $name
> ls
Mister Noodle
In bash, this would have created two directories "Mister" and "Noodle". In fish, it created only one: the variable had the value "Mister Noodle", so that is the argument that was passed to mkdir, spaces and all.

Exit Status

Unlike other shells, fish stores the exit status of the last command in $status instead of $?. 
> false
> echo $status
1
Zero is considered success, and non-zero is failure.

Exports (Environment Variables)

Unlike other shells, fish does not have an export command. Instead, a variable is exported via an option to set, either --export or just -x. 
> set -x MyVariable SomeValue
> env | grep MyVariable
MyVariable=SomeValue
You can erase a variable with -e or --erase 
> set -e MyVariable
> env | grep MyVariable
(no output)

Lists

The set command above used quotes to ensure that Mister Noodle was one argument. If it had been two arguments, then name would have been a list of length 2. In fact, all variables in fish are really lists, that can contain any number of values, or none at all.

Some variables, like $PWD, only have one value. By convention, we talk about that variable's value, but we really mean its first (and only) value.

Other variables, like $PATH, really do have multiple values. During variable expansion, the variable expands to become multiple arguments: 

> echo $PATH
/usr/bin /bin /usr/sbin /sbin /usr/local/bin

Lists cannot contain other lists: there is no recursion. A variable is a list of strings, full stop.

Get the length of a list with count: 

> count $PATH
5
You can append (or prepend) to a list by setting the list to itself, with some additional arguments. Here we append /usr/local/bin to $PATH: 
> set PATH $PATH /usr/local/bin
You can access individual elements with square brackets. Indexing starts at 1 from the beginning, and -1 from the end: 
> echo $PATH
/usr/bin /bin /usr/sbin /sbin /usr/local/bin
> echo $PATH[1]
/usr/bin
> echo $PATH[-1]
/usr/local/bin
You can also access ranges of elements, known as "slices:" 
> echo $PATH[1..2]
/usr/bin /bin
> echo $PATH[-1..2]
/usr/local/bin /sbin /usr/sbin /bin
You can iterate over a list (or a slice) with a for loop: 
> for val in $PATH
        echo "entry: $val"
  end
entry: /usr/bin/
entry: /bin
entry: /usr/sbin
entry: /sbin
entry: /usr/local/bin

Command Substitutions

Command substitutions use the output of one command as an argument to another. Unlike other shells, fish does not use backticks ` for command substitutions. Instead, it uses parentheses: 
> echo In (pwd), running (uname)
In /home/tutorial, running FreeBSD
A common idiom is to capture the output of a command in a variable: 
> set os (uname)
> echo $os
Linux
Command substitutions are not expanded within quotes. Instead, you can temporarily close the quotes, add the command substitution, and reopen them, all in the same argument: 
> touch "testing_"(date +%s)".txt"
> ls *.txt
testing_1360099791.txt

Combiners (And, Or, Not)

Unlike other shells, fish does not have special syntax like && or || to combine commands. Instead it has commands and, or, and not. 
> cp file1.txt file1_bak.txt; and echo "Backup successful"; or echo "Backup failed"
Backup failed

Conditionals (If, Else, Switch)

Use if, else if, and else to conditionally execute code, based on the exit status of a command. 
if grep fish /etc/shells
        echo Found fish
else if grep bash /etc/shells
        echo Found bash
else
        echo Got nothing
end
There is also a switch command: 
switch (uname)
        case Linux
                echo Hi Tux!
        case Darwin
                echo Hi Hexley!
        case FreeBSD NetBSD DragonFly
                echo Hi Beastie!
        case '*'
                echo Hi, stranger!
end
Note that case does not fall through, and can accept multiple arguments or (quoted) wildcards.

Functions

A fish function is a list of commands, which may optionally take arguments. Unlike other shells, arguments are not passed in "numbered variables" like $1, but instead in a single list $argv. To create a function, use the function builtin: 
> function say_hello
         echo Hello $argv
  end
> say_hello
Hello
> say_hello everybody!
Hello everybody!

Unlike other shells, fish does not have aliases or special prompt syntax. Functions take their place.

You can list the names of all functions with the functions keyword (note the plural!). fish starts out with a number of functions: 

> functions
alias, cd, delete-or-exit, dirh, dirs, down-or-search, eval, export, fish_command_not_found_setup, fish_config, fish_default_key_bindings, fish_prompt, fish_right_prompt, fish_sigtrap_handler, fish_update_completions, funced, funcsave, grep, help, history, isatty, ls, man, math, nextd, nextd-or-forward-word, open, popd, prevd, prevd-or-backward-word, prompt_pwd, psub, pushd, seq, setenv, sgrep, trap, type, umask, up-or-search, vared

You can see the source for any function by passing its name to functions: 

> functions ls
function ls --description 'List contents of directory'
        command ls -G $argv
end

Loops

While loops: 
> while true
        echo "Loop forever"
end
Loop forever
Loop forever
Loop forever
...
For loops can be used to iterate over a list. For example, a list of files: 
> for file in *.txt
        cp $file $file.bak
end
Iterating over a list of numbers can be done with `seq`: 
> for x in (seq 5)
        touch file_$x.txt
end

Prompt

Unlike other shells, there is no prompt variable like PS1. To display your prompt, fish executes a function with the name fish_prompt, and its output is used as the prompt. You can define your own prompt: 
> function fish_prompt
        echo "New Prompt % "
  end
New Prompt %
Multiple lines are OK. Colors can be set via set_color, passing it named ANSI colors, or hex RGB values: 
> function fish_prompt
        set_color purple
        date "+%m/%d/%y"
        set_color FF0
        echo (pwd) '>'
        set_color normal
  end
02/06/13
/home/tutorial >

You can choose among some sample prompts by running fish_config prompt. fish also supports RPROMPT through fish_right_prompt.

$PATH

$PATH is an environment variable containing the directories in which fish searches for commands. Instead of separating entries with a colon, $PATH is a list. You can modify $PATH in a few ways:

  1. By modifying the $fish_user_paths variable, which is automatically appended to $PATH. For example, to permanently add /usr/local/bin to your $PATH, you could write: 
    > set -U fish_user_paths $fish_user_paths /usr/local/bin
  2. Directly in config.fish (see below).

Startup (Where's .bashrc?)

fish starts by executing commands in ~/.config/fish/config.fish. You can create it if it does not exist.

It is possible to directly create functions and variables in config.fish file, using the commands shown above. For example: 

> cat ~/.config/fish/config.fish

set -x PATH $PATH /sbin/

function ll
    ls -lh $argv
end

However, it is more common and efficient to use autoloading functions and universal variables.

Autoloading Functions

When fish encounters a command, it attempts to autoload a function for that command, by looking for a file with the name of that command in ~/.config/fish/functions/.

For example, if you wanted to have a function ll, you would add a text file ll.fish to ~/.config/fish/functions: 

> cat ~/.config/fish/functions/ll.fish
function ll
        ls -lh $argv
end
This is the preferred way to define your prompt as well: 
> cat ~/.config/fish/functions/fish_prompt.fish
function fish_prompt
        echo (pwd) '> '
end

See the documentation for funced and funcsave for ways to create these files automatically.

Universal Variables

A universal variable is a variable whose value is shared across all instances of fish, now and in the future - even after a reboot. You can make a variable universal with set -U: 

> set -U EDITOR vim
Now in another shell: 
> echo $EDITOR
vim

Ready for more?

If you want to learn more about fish, there is lots of detailed documentation, an official mailing list, the IRC channel #fish on irc.oftc.net, and the github page.

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