.. _cmd-trap: trap - perform an action when the shell receives a signal ========================================================= Synopsis -------- .. synopsis:: trap [OPTIONS] [[ARG] REASON ... ] Description ----------- .. only:: builder_man NOTE: This page documents the fish builtin ``trap``. To see the documentation on any non-fish versions, use ``command man trap``. ``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 :ref:`event handler <event>`. 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.