```{index} single: sigtrap (pragma) ``` # sigtrap Perl pragma to enable simple signal handling ## SYNOPSIS ```perl 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 three 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](core/perlvar.md) 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: ```perl use sigtrap; ``` Ditto: ```perl use sigtrap qw(stack-trace old-interface-signals); ``` Provide a stack trace on the 4 listed signals only: ```perl use sigtrap qw(BUS SEGV PIPE ABRT); ``` Die on INT or QUIT: ```perl use sigtrap qw(die INT QUIT); ``` Die on HUP, INT, PIPE or TERM: ```perl 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: ```perl use sigtrap qw(die untrapped normal-signals); ``` Die on receipt one of any of the **normal-signals** which is currently **untrapped**, provide a stack trace on receipt of **any** of the **error-signals**: ```perl use sigtrap qw(die untrapped normal-signals stack-trace any error-signals); ``` Install my\_handler() as the handler for the **normal-signals**: ```perl 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: ```perl use sigtrap qw(handler my_handler normal-signals stack-trace error-signals); ```