my $last-total = 0;
my $last-idle = 0;
loop {
my $Δ-total = (my $this-total = [+] my @cpu = "/proc/stat".IO.lines[0].words[1..*]) - $last-total;
my $Δ-idle = (my $this-idle = @cpu[3]) - $last-idle;
$last-total = $this-total;
$last-idle = $this-idle;
print "\b" x 40, (100 * (1 - $Δ-idle / $Δ-total)).fmt("Utilization: %0.1f%% ");
sleep(1);
}