How to catch and handle a signal in Perl

Last updated on June 22, 2020 by Dan Nanni

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 handlern";
    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.

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