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[Anonymous Monk]

Then simply extend the search/replace pattern. Since this is just cosmetics, it is not detrimental if it fails. Here is a complete example. Run this code and it will become clear what is going on:

$c1=$c2=$c3=111222333444555;

$c1=~ s/^(-?\d+)(\d{3})(\d{3})/$1,$2,$3/; 
$c2=~ s/^(-?\d+)(\d{3})(\d{3})(\d{3})/$1,$2,$3,$4/; 
$c3=~ s/^(-?\d+)(\d{3})(\d{3})(\d{3})(\d{3})/$1,$2,$3,$4,$5/; 

print<<END;
$c1
$c2
$c3
END

[Biker]

It doesn't automatically scale. You must write that code with the knowledge of what is the biggest number you will handle.

"Since this is just cosmetics, it is not detrimental if it fails."

My users beg to disagree. Numbers not formatted correctly when presented on our Intranet Web pages may have a very high economical impact, including failed trades, penalty fees and loss of reputation.

The right answer is here.

[Anonymous Monk]

What do you mean "Right answer"? There are many ways of doing things in perl. You don't have get snotty about it. Here is yet another way that is even more efficent then your "right answer", but not as efficent as my previous example:

&commify($x);#Robust - Does all size numbers

sub commify {
local $_ = shift;
1 while s/(-?\d+)(\d{3})/$1,$2/;
return $_;
}