my $start_time = time;
sub exec_time { return time - $start_time }
my $cmd = 'sleep 3600 ; echo "yawn"';
my $yawn;
my $cmd_pid = open my $cmd_fh, '-|', $cmd
    or die "Can't run '$cmd': $!\n";
eval {
    local $SIG{ALRM} = sub { kill 15, $cmd_pid; die "alarm\n" };
    alarm 5;
    $yawn = do { local $/; <$cmd_fh> };
    alarm 0;
};
close $cmd_fh;
printf "(%d) yawn?  $yawn", exec_time();
__END__
(5) yawn?