use strict;
use warnings;

while()
{
   my @loads;
   my $i = my $cpuload = 0;
   open(INFIL,"< /proc/stat") || die("Unable To Open /proc/stat\n");
   <INFIL> =~ /^cpu\s+(\d+)\s+(\d+)\s+(\d+).*/;
   @loads  = ($1, $2, $3);
   sleep 1;
   seek INFIL, 0, 0;
   <INFIL> =~ /^cpu\s+(\d+)\s+(\d+)\s+(\d+).*/;
   foreach ($1, $2, $3) { $cpuload += $_ - $loads[$i++]; }
   close(INFIL);

   print "$cpuload\n";

}
[download]

Tie::File looks interesting, so that might not be the final version ;)

Thanks a lot folks!