in reply to How do I add commas to a number?
This regexp will add commas to numbers: s/(^[-+]?\d+?(?=(?>(?:\d{3})+)(?!\d))|\G\d{3}(?=\d))/$1,/g; [download]
s/(^[-+]?\d+?(?=(?>(?:\d{3})+)(?!\d))|\G\d{3}(?=\d))/$1,/g; [download]
Originally posted as a Categorized Answer.