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!
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.
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.
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 shell variables Synopsis...
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.
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.
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
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 → or Control-F. To accept a single word of the autosuggestion, Alt-→ (right arrow). If the autosuggestion is not what you want, just ignore it.
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!
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.
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.
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)
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 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
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
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.
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
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
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 is an environment variable containing the directories in which fish searches for commands. Unlike other shells, $PATH is a list, not a colon-delimited string.
To prepend to $PATH, you can write:
> set PATH /new/path $PATH
You can do so directly in fish.config, like you might do in other shells with .profile. See this example.
A faster way is to modify the $fish_user_paths universal variable, which is automatically prepended to $PATH. For example, to permanently add /usr/local/bin to your $PATH, you could write:
> set -U fish_user_paths /usr/local/bin $fish_user_paths
The advantage is that you don't have to go mucking around in files: just run this once at the command line, and it will affect the current session and all future instances too. (Note: you should NOT add this line to fish.config. If you do, the variable will get longer each time you run fish!)
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.
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.
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
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.