Perl FAQ 4.34: How can I print out a number with commas into it?

Perl FAQ 4.34

How can I print out a number with commas into it?

This one will do it for you: 

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



$n = 23659019423.2331;
print "GOT: ", &commify($n), "\n";



GOT: 23,659,019,423.2331

The reason you can't just do 

    s/^(-?\d+)(\d{3})/$1,$2/g;
Is that you have to put the comma in and then recalculate anything. Some substitutions need to work this way. See the question on expanding tabs for another such.

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