\section trap trap - perform an action when the shell receives a signal

\subsection trap-synopsis Synopsis
<tt>trap [OPTIONS] [[ARG] SIGSPEC ... ]</tt>

\subsection trap-description Description

Trap is a shellscript wrapper around the fish event delivery
framework. It exists for backwards compatibility with Posix
shells. For other uses, it is recommended to define a <a
href='index.html#event'>event handler</a>.

- ARG is the command to be executed on signal delivery
- SIGSPEC is the name of the signal to trap
- \c -h or \c --help Display help and exit
- \c -l or \c --list-signals print a list of signal names
- \c -p or \c --print print all defined signal handlers

If ARG and SIGSPEC are both specified, ARG is the command to be
executed when the signal specified by SIGSPEC is delivered.

If ARG is absent (and there is a single SIGSPEC) 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 SIGSPEC 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 SIGSPEC 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 return status is 1 if any SIGSPEC is invalid; otherwise trap
returns 0.