trap - perform an action when the shell receives a signal


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


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 is the command to be executed on signal delivery.
  • REASON is the 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.

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.

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


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