my $start = time;
sub exec_time { return time - $start }
alarm 5;
$SIG{ALRM} = sub { printf "alarm (%d)!\n", exec_time() };
my $yawn = `sleep 10 ; echo "yawn"`;
printf "(%d) yawn?  $yawn\n", exec_time();
__END__
alarm (5)!
(10) yawn?  yawn