#/usr/bin/env perl
use strict;
use warnings;

# We need sub-second precision here :-)
use Time::HiRes wq(time sleep);

my $lastrun = 0;
while(1) {
    # Time consuming stuff here

     my $now = time;
     # Calculate the time we need to sleep. First we calculate the difference between now and the last run.
     # That's how long the last run took. Now, calculate how many seconds remaining in the current minute.
     # If the answer is negative, one of two things happened: Either it's our first run, or the last run took
     # longer than a minute
     my $sleeptime = 60 - ($now - $lastrun);
     if($sleeptime > 0) {
         sleep($sleeptime);
     }
     $lastrun = $now;
}
##</code><code>##

#/usr/bin/env perl
use strict;
use warnings;

# We need sub-second precision here :-)
use Time::HiRes wq(time sleep);

my $activesecond = 42; # Run whenever the seconds are "42"

while(1) {
    my $now = time;

    # The built-in modulus function converts to integer,
    # which would introduce jitter of up to nearly a second.
    # So, out with the traditional:
    # my $cursecond = $now % 60;
    # ...and in with the more manual version:
    my $cursecond = $now - (60.0 * int($now / 60.0));

    if($cursecond != $activesecond) {
        # Need to wait
        my $sleeptime = $activesecond - $cursecond;
        if($sleeptime < 0) {
            # Handle rollover
            $sleeptime += 60.0;
        }
        sleep($sleeptime);
    }

    # Time consuming stuff here
}
##</code><code>##

my $taioffset = 37;

...

    my $now = $time + $taioffset;