Any signal, or at least any non-ignored signal interrupts sleep.

Many forget this, and expect that a literal sleep 60 may not actually take 60s, but could be anything less than that. In one-off scripts I've seen code like this (untested):

sub my_sleep {
    my $sleep_time = (shift or 1); # total time to sleep
    my $sleep_interval = (shift or 10); # wake up at least this often
    my $start = time;
    $stop_time = $start + $sleep_time;
    while (time < $stop_time) {
        sleep $sleep_time;
        # handle wake up tasks
    }
    my $elapsed = time - $start;
    return $elapsed; # total time actually slept (plus shipping and ha
+ndling)
}
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You may want additional conditions, and use this as a timeout mechanism. There's probably a nice module for that, or roll your own.

But the point is sleep comes with an unspoken if (...), if something else doesn't wake me up.