That's not a working regex. The best ones work something like this: 
$number=1234567; # with commas, should be "1,234,567" 
$number =~ s/(\d)(?=(\d{3})+(\D|$))/$1\,/g;

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Notice the missing inner repetition in the previous post? And I'm doing this with lookahead, so I can scan from left to right. The "1 while ..." solutions scan effectively from right to left, so they may be slower. Actually, I'd be interested in the various benchmarks on these. {grin}

-- Randal L. Schwartz, Perl hacker

In reply to RE: regexp for adding commas to a number by merlyn
in thread regexp for adding commas to a number by Kozz

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