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47 lines
1.7 KiB
ReStructuredText
47 lines
1.7 KiB
ReStructuredText
.. _cmd-trap:
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trap - perform an action when the shell receives a signal
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=========================================================
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Synopsis
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--------
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trap [OPTIONS] [[ARG] REASON ... ]
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Description
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-----------
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``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>`.
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The following parameters are available:
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- ``ARG`` is the command to be executed on signal delivery.
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- ``REASON`` is the name of the event to trap. For example, a signal like ``INT`` or ``SIGINT``, or the special symbol ``EXIT``.
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- ``-l`` or ``--list-signals`` prints a list of signal names.
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- ``-p`` or ``--print`` prints all defined signal handlers.
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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).
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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.
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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.
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Signal names are case insensitive and the ``SIG`` prefix is optional.
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The return status is 1 if any ``REASON`` is invalid; otherwise trap returns 0.
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Example
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-------
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::
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trap "status --print-stack-trace" SIGUSR1
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# Prints a stack trace each time the SIGUSR1 signal is sent to the shell.
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