time() returns number of seconds since the epoch so to figure out if there is a difference of more than 12 hours all you have to do is check for the difference using seconds (12hours = 60*60*12).

if ($current_time - $oldtime > 43200)
{
    print "There is > 12 hour difference\n";
}
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If you need to do more complex date/time calculations you may benefit from the many date modules on CPAN.

(With localtime, you get an "argument isn't numeric in subtraction" error.)

#filename: stickOutputOnEnd.pl
use warnings;
use strict;

my $time1 = time();
sleep(5);
my $time2 = time();
my $timedifference = $time2-$time1; # doesn't work if you use localtim
+e.
print scalar $timedifference;
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FWIW, this works with time(), but not localtime().

Er, yes. Because they have two quite distinct functions. time() returns the epoch seconds representing the current time and localtime() (or gmtime()) returns a list representing the parts of the time (like the struct tm returned by the similarly named C library functions.) when in list context or a string represention thereof when in scalar context.

/J\

Thank you all. That really helps.