Woohoo!

I can help for once! As I found previously!

$number=1234567; # with commas, should be "1,234,567" 
$number =~ s/(\d)(?=(\d{3})+(\D|$))/$1\,/g;
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Node:
http://www.perlmonks.com/index.pl?node_id=28331&lastnode_id=864