A "signal" is a way for your program to process "asynchronous" events. Meaning that you register a subroutine to be called when that event occurs. When you do this, you don't have to explictly keep checking that a particular event occured, the OS will call the sub when that event occurs.

kill ALRM, $$ doesn't make sense to me!

The below code shows a simple example of a handler for SIGALRM. 

#!/usr/bin/perl -w
use strict;
#$|=1; #see note below...

$SIG{'ALRM'} = 'timeout';

alarm(1);
while (1){sleep(1);} 

sub timeout
{
    print        "stdout: Alarming!\n";
    print STDERR "stderr: Alarming!\n";
    exit(0);
};
__END__
prints:
   Note: stderr msg comes first because "autoflush" for
   stdout wasn't turned on (stdout normally doesn't
   get "flushed" until program end). 
   $|=1; turns autoflush on.

stderr: Alarming!
stdout: Alarming!

[download]
Kill $some_number makes no sense if $some_number is not a PID. kill ALRM doesn't have a PID. ALRM on my system is "numeric 14", but that is just shorthand for what the string ALRM means.

In reply to Re: Signals in Strawberry Perl: Name or number? by Marshall
in thread Signals in Strawberry Perl: Name or number? by bv

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