I don't want an argument with tirwhan over whether this is good or not, but this works on my linux box, It was posted a few years ago( not my invention).

#!/usr/bin/perl
#Description:  These subs allow you control how much % CPU maximum wil
+l use your script. CPU_start() must be called once when you script st
+art.
#This example script will use 30% CPU until Ctrl-C pressed:

CPU_start(); CPU_max(30) while 1;

use Time::HiRes qw(time);

sub CPU_used {
(map {$_->[13]+$_->[14]}
[split " ", Cat("/proc/self/stat")])[0]
}

{ my %start = (tm => 0, cpu => 0);
sub CPU_start { @start{"tm","cpu"} = (time(),CPU_used()) }
sub CPU_max {
my ($max, $real, $cpu) = ($_[0], time()-$start{tm},
CPU_used()-$start{cpu});
return unless defined($max) and $max > 0;
&sleep( $cpu/$max-$real );
}}

#
# macro used from CPU_used() and CPU_max()
#

sub sleep { select undef,undef,undef,$_[0] }
sub Cat {
local *F;
open F, "< ".$_[0] or return;
local $/ unless wantarray;
return <F>;
}
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