APM: Question: breaking up a numeric variable

[Marc Majcher]

"Goldilox" <Goldilox at teachnet.edb.utexas.edu>:
:
:Is there a good way to take a numeric variable of undetermined length
:and print it out with a comma appropriately placed at every third character
:slot from the end
:

'perldoc -q comma' gives us this:

Found in /usr/local/lib/perl5/5.6.1/pod/perlfaq5.pod

       How can I output my numbers with commas added?

       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

       You can't just:

           s/^([-+]?\d+)(\d{3})/$1,$2/g;

       because you have to put the comma in and then recalculate
       your position.

       Alternatively, this code commifies all numbers in a line
       regardless of whether they have decimal portions, are
       preceded by + or -, or whatever:

           # from Andrew Johnson <ajohnson at gpu.srv.ualberta.ca>
           sub commify {
              my $input = shift;
               $input = reverse $input;
               $input =~ s<(\d\d\d)(?=\d)(?!\d*\.)><$1,>g;
               return scalar reverse $input;
           }


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