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.\" ========================================================================
.\"
.IX Title "sigtrap 3perl"
.TH sigtrap 3perl "2021-09-24" "perl v5.32.1" "Perl Programmers Reference Guide"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
sigtrap \- Perl pragma to enable simple signal handling
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 11
\&    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 \*(Aqhandler\*(Aq => \e&my_handler, \*(Aqnormal\-signals\*(Aq;
\&    use sigtrap qw(handler my_handler normal\-signals
\&                    stack\-trace error\-signals);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
The \fBsigtrap\fR pragma is a simple interface to installing signal
handlers.  You can have it install one of two handlers supplied by
\&\fBsigtrap\fR itself (one which provides a Perl stack trace and one which
simply \f(CW\*(C`die()\*(C'\fRs), 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.
.PP
The arguments passed to the \f(CW\*(C`use\*(C'\fR statement which invokes \fBsigtrap\fR
are processed in order.  When a signal name or the name of one of
\&\fBsigtrap\fR's signal lists is encountered a handler is immediately
installed, when an option is encountered it affects subsequently
installed handlers.
.SH "OPTIONS"
.IX Header "OPTIONS"
.SS "\s-1SIGNAL HANDLERS\s0"
.IX Subsection "SIGNAL HANDLERS"
These options affect which handler will be used for subsequently
installed signals.
.IP "\fBstack-trace\fR" 4
.IX Item "stack-trace"
The handler used for subsequently installed signals outputs a Perl stack
trace to \s-1STDERR\s0 and then tries to dump core.  This is the default signal
handler.
.IP "\fBdie\fR" 4
.IX Item "die"
The handler used for subsequently installed signals calls \f(CW\*(C`die\*(C'\fR
(actually \f(CW\*(C`croak\*(C'\fR) with a message indicating which signal was caught.
.IP "\fBhandler\fR \fIyour-handler\fR" 4
.IX Item "handler your-handler"
\&\fIyour-handler\fR will be used as the handler for subsequently installed
signals.  \fIyour-handler\fR can be any value which is valid as an
assignment to an element of \f(CW%SIG\fR. See perlvar for examples of
handler functions.
.SS "\s-1SIGNAL LISTS\s0"
.IX Subsection "SIGNAL LISTS"
\&\fBsigtrap\fR has a few built-in lists of signals to trap.  They are:
.IP "\fBnormal-signals\fR" 4
.IX Item "normal-signals"
These are the signals which a program might normally expect to encounter
and which by default cause it to terminate.  They are \s-1HUP, INT, PIPE\s0 and
\&\s-1TERM.\s0
.IP "\fBerror-signals\fR" 4
.IX Item "error-signals"
These signals usually indicate a serious problem with the Perl
interpreter or with your script.  They are \s-1ABRT, BUS, EMT, FPE, ILL,
QUIT, SEGV, SYS\s0 and \s-1TRAP.\s0
.IP "\fBold-interface-signals\fR" 4
.IX Item "old-interface-signals"
These are the signals which were trapped by default by the old
\&\fBsigtrap\fR interface, they are \s-1ABRT, BUS, EMT, FPE, ILL, PIPE, QUIT,
SEGV, SYS, TERM,\s0 and \s-1TRAP.\s0  If no signals or signals lists are passed to
\&\fBsigtrap\fR, this list is used.
.PP
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.
.SS "\s-1OTHER\s0"
.IX Subsection "OTHER"
.IP "\fBuntrapped\fR" 4
.IX Item "untrapped"
This token tells \fBsigtrap\fR to install handlers only for subsequently
listed signals which aren't already trapped or ignored.
.IP "\fBany\fR" 4
.IX Item "any"
This token tells \fBsigtrap\fR to install handlers for all subsequently
listed signals.  This is the default behavior.
.IP "\fIsignal\fR" 4
.IX Item "signal"
Any argument which looks like a signal name (that is,
\&\f(CW\*(C`/^[A\-Z][A\-Z0\-9]*$/\*(C'\fR) indicates that \fBsigtrap\fR should install a
handler for that name.
.IP "\fInumber\fR" 4
.IX Item "number"
Require that at least version \fInumber\fR of \fBsigtrap\fR is being used.
.SH "EXAMPLES"
.IX Header "EXAMPLES"
Provide a stack trace for the old-interface-signals:
.PP
.Vb 1
\&    use sigtrap;
.Ve
.PP
Ditto:
.PP
.Vb 1
\&    use sigtrap qw(stack\-trace old\-interface\-signals);
.Ve
.PP
Provide a stack trace on the 4 listed signals only:
.PP
.Vb 1
\&    use sigtrap qw(BUS SEGV PIPE ABRT);
.Ve
.PP
Die on \s-1INT\s0 or \s-1QUIT:\s0
.PP
.Vb 1
\&    use sigtrap qw(die INT QUIT);
.Ve
.PP
Die on \s-1HUP, INT, PIPE\s0 or \s-1TERM:\s0
.PP
.Vb 1
\&    use sigtrap qw(die normal\-signals);
.Ve
.PP
Die on \s-1HUP, INT, PIPE\s0 or \s-1TERM,\s0 except don't change the behavior for
signals which are already trapped or ignored:
.PP
.Vb 1
\&    use sigtrap qw(die untrapped normal\-signals);
.Ve
.PP
Die on receipt one of an of the \fBnormal-signals\fR which is currently
\&\fBuntrapped\fR, provide a stack trace on receipt of \fBany\fR of the
\&\fBerror-signals\fR:
.PP
.Vb 2
\&    use sigtrap qw(die untrapped normal\-signals
\&                    stack\-trace any error\-signals);
.Ve
.PP
Install \fBmy_handler()\fR as the handler for the \fBnormal-signals\fR:
.PP
.Vb 1
\&    use sigtrap \*(Aqhandler\*(Aq, \e&my_handler, \*(Aqnormal\-signals\*(Aq;
.Ve
.PP
Install \fBmy_handler()\fR as the handler for the normal-signals, provide a
Perl stack trace on receipt of one of the error-signals:
.PP
.Vb 2
\&    use sigtrap qw(handler my_handler normal\-signals
\&                    stack\-trace error\-signals);
.Ve