How to catch and handle a signal in Perl

Question: I need to handle an interrupt signal by using a custom signal handler in Perl. In general, how can I catch and handle various signals (e.g., INT, TERM) in a Perl program?

As an asynchronous notification mechanism in the POSIX standard, a signal is sent by an operating system to a process to notify it of a certain event. When a signal is generated, the target process's execution is interrupted by an operating system, and the signal is delivered to the process's signal handler routine. One can define and register a custom signal handler or rely on the default signal handler.

In Perl, signals can be caught and handled by using a global %SIG hash variable. This %SIG hash variable is keyed by signal numbers, and contains references to corresponding signal handlers. Therefore, if you want to define a custom signal handler for a particular signal, you can simply update the hash value of %SIG for the signal.

Here is a code snippet to handle interrupt (INT) and termination (TERM) signals using a custom signal handler.

$SIG{INT}  = \&signal_handler;
$SIG{TERM} = \&signal_handler;

sub signal_handler {
    print "This is a custom signal handler\n";
    die "Caught a signal $!";
}

Other valid hash values for %SIG are 'IGNORE' and 'DEFAULT'. When an assigned hash value is 'IGNORE' (e.g., $SIG{CHLD}='IGNORE'), the corresponding signal will be ignored. Assigning 'DEFAULT' hash value (e.g., $SIG{HUP}='DEFAULT') means that we will be using a default signal handler.

Download this article as ad-free PDF (made possible by your kind donation): 
Download PDF

Subscribe to Ask Xmodulo

Do you want to receive Linux related questions & answers published at Ask Xmodulo? Enter your email address below, and we will deliver our Linux Q&A straight to your email box, for free. Delivery powered by Google Feedburner.


Support Xmodulo

Did you find this tutorial helpful? Then please be generous and support Xmodulo!

Leave a comment

Your email address will not be published. Required fields are marked *