function - create a function¶
function NAME [OPTIONS]; BODY; end
function creates a new function
NAME with the 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:
--argument-names NAMESassigns the value of successive command-line arguments to the names given in NAMES.
--description=DESCRIPTIONis a description of what the function does, suitable as a completion description.
--wraps=WRAPPED_COMMANDcauses the function to inherit completions from the given wrapped command. See the documentation for complete for more information.
--on-event EVENT_NAMEtells fish to run this function when the specified named event is emitted. Fish internally generates named events e.g. when showing the prompt.
--on-variable VARIABLE_NAMEtells fish to 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).
--on-job-exit PIDtells fish to run this function when the job containing a child process with the given PID exits. Instead of PID, the string 'caller' can be specified. This is only legal when in a command substitution, and will result in the handler being triggered by the exit of the job which created this command substitution.
--on-process-exit PIDtells fish to 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.
--on-signal SIGSPECtells fish to 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).
--no-scope-shadowingallows 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-shadowingthe 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.
--inherit-variable NAMEsnapshots the value of the variable
NAMEand 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 notifyexample below for how this might be used.
If the user enters any additional arguments after the function, they are inserted into the environment variable list
$argv. If the
--argument-names option is provided, the arguments are also assigned to names specified in that option.
By using one of the event handler switches, a function can be made to run automatically at specific events. The user may generate new events using the emit builtin. Fish generates the following named events:
fish_prompt, which is emitted whenever a new fish prompt is about to be displayed.
fish_preexec, which is emitted right before executing an interactive command. The commandline is passed as the first parameter. Not emitted if command is empty.
fish_posterror, which is emitted right after executing a command with syntax errors. The commandline is passed as the first parameter.
fish_postexec, which is emitted right after executing an interactive command. The commandline is passed as the first parameter. Not emitted if command is empty.
fish_exitis emitted right before fish exits.
fish_cancel, which is emitted when a commandline is cleared (used for terminal-shell integration).
function ll ls -l $argv end
will run the
ls command, using the
-l option, while passing on any additional files and switches to
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.
Events are only received from the current fish process as there is no way to send events from one fish process to another.