trap - perform an action when the shell receives a signal — fish-shell 3.5.1 documentation

# trap - perform an action when the shell receives a signal

## Synopsis

    trap [OPTIONS] [[ARG] REASON ... ]

## Description

`trap` is a wrapper around the fish event delivery framework. It exists for backwards compatibility with POSIX shells. For other uses, it is recommended to define an event handler.

The following parameters are available:

ARG

  Command to be executed on signal delivery.

REASON

  Name of the event to trap. For example, a signal like `INT` or `SIGINT`, or the special symbol `EXIT`.

-l or --list-signals

  Prints a list of signal names.

-p or --print

  Prints all defined signal handlers.

-h or --help

  Displays help about using this command.

If ARG and REASON are both specified, ARG is the command to be executed when the event specified by REASON occurs (e.g., the signal is delivered).

If ARG is absent (and there is a single REASON) or `-`, each specified signal is reset to its original disposition (the value it had upon entrance to the shell). If ARG is the null string the signal specified by each REASON is ignored by the shell and by the commands it invokes.

If ARG is not present and -p has been supplied, then the trap commands associated with each REASON are displayed. If no arguments are supplied or if only -p is given, `trap` prints the list of commands associated with each signal.

Signal names are case insensitive and the `SIG` prefix is optional. Trapping a signal will prevent fish from exiting in response to that signal.

The exit status is 1 if any REASON is invalid; otherwise trap returns 0.

## Example

    trap "status --print-stack-trace" SIGUSR1
    # Prints a stack trace each time the SIGUSR1 signal is sent to the shell.