FUNCTION(1)

NAME
function - create a function

SYNOPSIS
function NAME [OPTIONS]; BODY; end

DESCRIPTION

function creates a new function NAME with the body BODY.

A function is a list of commands that will be executed when the name of the function is given as a command.

The following options are available:

-a NAMES or --argument-names NAMES
    Assigns the value of successive command-line arguments to the names given in NAMES (separated by spaces). These are the same arguments given in argv <#envvar-argv>, and are still available there (unless --inherit-variable argv was used or one of the given NAMES is argv). See also Argument Handling <#variables-argv>.

-d DESCRIPTION or --description DESCRIPTION
    A description of what the function does, suitable as a completion description.

-w WRAPPED_COMMAND or --wraps WRAPPED_COMMAND
    Inherit completions from the given WRAPPED_COMMAND. This is used to say that this function completes like that command, for example if you're creating an alias. See the documentation for complete <> for more information. If the wrapped command is the same as the function name, this will be ignored.

-e EVENT_NAME or --on-event EVENT_NAME
    Run this function when the specified named event is emitted. fish internally generates named events, for example, when showing the prompt. Custom events can be emitted using the emit <> command.

-v VARIABLE_NAME or --on-variable VARIABLE_NAME
    Run this function when the variable VARIABLE_NAME changes value. Note that fish makes no guarantees on any particular timing or even that the function will be run for every single set. Rather it will be run when the variable has been set at least once, possibly skipping some values or being run when the variable has been set to the same value (except for universal variables set in other shells - only changes in the value will be picked up for those).

-j PID or --on-job-exit PID
    Run this function when the job containing a child process with the given process ID PID exits. Instead of a PID, the string 'caller' can be specified. This is only allowed when in a command substitution, and will result in the handler being triggered by the exit of the job which created this command substitution. This will not trigger for disowned <> jobs.

-p PID or --on-process-exit PID
    Run this function when the fish child process with process ID PID exits. Instead of a PID, for backward compatibility, "%self" can be specified as an alias for $fish_pid, and the function will be run when the current fish instance exits. This will not trigger for disowned <> jobs.

-s SIGSPEC or --on-signal SIGSPEC
    Run this function when the signal SIGSPEC is delivered. SIGSPEC can be a signal number, or the signal name, such as SIGHUP (or just HUP). Note that the signal must have been delivered to fish; for example, ctrl-c sends SIGINT to the foreground process group, which will not be fish if you are running another command at the time. Observing a signal will prevent fish from exiting in response to that signal.

-S or --no-scope-shadowing
    Allows the function to access the variables of calling functions. Normally, any variables inside the function that have the same name as variables from the calling function are "shadowed", and their contents are independent of the calling function.

    It's important to note that this does not capture referenced variables or the scope at the time of function declaration! At this time, fish does not have any concept of closures, and variable lifetimes are never extended. In other words, by using --no-scope-shadowing the scope of the function each time it is run is shared with the scope it was called from rather than the scope it was defined in.

-V or --inherit-variable NAME
    Snapshots the value of the variable NAME and defines a local variable with that same name and value when the function is defined. This is similar to a closure in other languages like Python but a bit different. Note the word "snapshot" in the first sentence. If you change the value of the variable after defining the function, even if you do so in the same scope (typically another function) the new value will not be used by the function you just created using this option. See the function notify example below for how this might be used.

    The event handler switches (on-event, on-variable, on-job-exit, on-process-exit and on-signal) cause a function to run automatically at specific events. New named events for --on-event can be fired using the emit <> builtin. fish already generates a few events, see Event handlers <#event> for more.

    Functions names cannot be reserved words. These are elements of fish syntax or builtin commands which are essential for the operations of the shell. Current reserved words are [, _, and, argparse, begin, break, builtin, case, command, continue, else, end, eval, exec, for, function, if, not, or, read, return, set, status, string, switch, test, time, and while.

    Care should be taken when creating a function of the same name as an existing shell builtin or common program. If the function behaves differently, it is very common for problems to occur within fish or in scripts written by others. Consider writing an abbreviation <> if you are wanting to replace one tool with another for interactive use.

EXAMPLE

    function ll
        ls -l $argv
    end

will run the ls command, using the -l option, while passing on any additional files and switches to ls.

    function debug -a name val
        echo [DEBUG] $name: $val >&2
    end
    set foo bar
    debug foo bar
    # prints: [DEBUG] foo: bar
    # OR
    function debug2 -a var
        echo [DEBUG] $var: $$var >&2
    end
    set foo bar
    debug2 foo
    # prints: [DEBUG] foo: bar

will create a debug command to print chosen variables to stderr.

    function mkdir -d "Create a directory and set CWD"
        command mkdir $argv
        if test $status = 0
            switch $argv[(count $argv)]
                case '-*'
                case '*'
                    cd $argv[(count $argv)]
                    return
            end
        end
    end

This will run the mkdir command, and if it is successful, change the current working directory to the one just created.

    function notify
        set -l job (jobs -l -g)
        or begin; echo "There are no jobs" >&2; return 1; end
        function _notify_job_$job --on-job-exit $job --inherit-variable job
            echo -n \a # beep
            functions -e _notify_job_$job
        end
    end

This will beep when the most recent job completes.

NOTES

Events are only received from the current fish process as there is no way to send events from one fish process to another.

SEE MORE

For more explanation of how functions fit into fish, see Functions <#syntax-function>.

Copyright
fish-shell developers