The following subroutine, with a one-line join, should do the trick:

sub PrettyTime {
  my $s = int(shift);
  join(', ', reverse map {my $t = $s % $_->[0]; $s /= $_->[0]; $t.$_->
+[1].($t > 1 ? 's' : '')} ([60, ' sec'], [60, ' min'], [24, ' hr'], [9
+999999, ' day']))
}
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Limitations are integer seconds and up to 9999999 days. Both would be easy to remedy. But it does handle singular and plural units. For example, print PrettyTime(1234561) prints 14 days, 6 hrs, 56 mins, 1 sec Eliminating zeroes is harder, though, because join sticks its delimiter in even when map returns undef. Leading zeroes are no easier either, because map doesn't respond to a last. For these you might have to resort to a foreach with an internal unshift (eliminates the reverse) into a results array. Then do the join.