sigtrap

Section: Perl Programmers Reference Guide (3pm)
Updated: 2021-03-31
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NAME

sigtrap - Perl pragma to enable simple signal handling

SYNOPSIS

    use sigtrap;
    use sigtrap qw(stack-trace old-interface-signals);  # equivalent
    use sigtrap qw(BUS SEGV PIPE ABRT);
    use sigtrap qw(die INT QUIT);
    use sigtrap qw(die normal-signals);
    use sigtrap qw(die untrapped normal-signals);
    use sigtrap qw(die untrapped normal-signals
                    stack-trace any error-signals);
    use sigtrap 'handler' => \&my_handler, 'normal-signals';
    use sigtrap qw(handler my_handler normal-signals
                    stack-trace error-signals);

DESCRIPTION

The sigtrap pragma is a simple interface to installing signal handlers. You can have it install one of two handlers supplied by sigtrap itself (one which provides a Perl stack trace and one which simply "die()"s), or alternately you can supply your own handler for it to install. It can be told only to install a handler for signals which are either untrapped or ignored. It has a couple of lists of signals to trap, plus you can supply your own list of signals.

The arguments passed to the "use" statement which invokes sigtrap are processed in order. When a signal name or the name of one of sigtrap's signal lists is encountered a handler is immediately installed, when an option is encountered it affects subsequently installed handlers.

OPTIONS

SIGNAL HANDLERS

These options affect which handler will be used for subsequently installed signals.

stack-trace: The handler used for subsequently installed signals outputs a Perl stack trace to STDERR and then tries to dump core. This is the default signal handler.
die: The handler used for subsequently installed signals calls "die" (actually "croak") with a message indicating which signal was caught.
handler your-handler: your-handler will be used as the handler for subsequently installed signals. your-handler can be any value which is valid as an assignment to an element of %SIG. See perlvar for examples of handler functions.

SIGNAL LISTS

sigtrap has a few built-in lists of signals to trap. They are:

normal-signals: These are the signals which a program might normally expect to encounter and which by default cause it to terminate. They are HUP, INT, PIPE and TERM.
error-signals: These signals usually indicate a serious problem with the Perl interpreter or with your script. They are ABRT, BUS, EMT, FPE, ILL, QUIT, SEGV, SYS and TRAP.
old-interface-signals: These are the signals which were trapped by default by the old sigtrap interface, they are ABRT, BUS, EMT, FPE, ILL, PIPE, QUIT, SEGV, SYS, TERM, and TRAP. If no signals or signals lists are passed to sigtrap, this list is used.

For each of these three lists, the collection of signals set to be trapped is checked before trapping; if your architecture does not implement a particular signal, it will not be trapped but rather silently ignored.

OTHER

untrapped: This token tells sigtrap to install handlers only for subsequently listed signals which aren't already trapped or ignored.
any: This token tells sigtrap to install handlers for all subsequently listed signals. This is the default behavior.
signal: Any argument which looks like a signal name (that is, "/^[A-Z][A-Z0-9]*$/") indicates that sigtrap should install a handler for that name.
number: Require that at least version number of sigtrap is being used.

EXAMPLES

Provide a stack trace for the old-interface-signals:

    use sigtrap;

Ditto:

    use sigtrap qw(stack-trace old-interface-signals);

Provide a stack trace on the 4 listed signals only:

    use sigtrap qw(BUS SEGV PIPE ABRT);

Die on INT or QUIT:

    use sigtrap qw(die INT QUIT);

Die on HUP, INT, PIPE or TERM:

    use sigtrap qw(die normal-signals);

Die on HUP, INT, PIPE or TERM, except don't change the behavior for signals which are already trapped or ignored:

    use sigtrap qw(die untrapped normal-signals);

Die on receipt one of an of the normal-signals which is currently untrapped, provide a stack trace on receipt of any of the error-signals:

    use sigtrap qw(die untrapped normal-signals
                    stack-trace any error-signals);

Install my_handler() as the handler for the normal-signals:

    use sigtrap 'handler', \&my_handler, 'normal-signals';

Install my_handler() as the handler for the normal-signals, provide a Perl stack trace on receipt of one of the error-signals:

    use sigtrap qw(handler my_handler normal-signals
                    stack-trace error-signals);