#!/usr/bin/perl -l
use strict;
use warnings;

my @numbers = ( 23, '1,234', '2,2', '12,234,567', -1, '-12,234',
   '-23,23', '999,999', 0 );

foreach my $number (@numbers) {
   if (my @sections = $number =~ /^(-?\d{1,3})(?:,(\d\d\d))*$/) {
       print join '', grep {defined} @sections;
   }
   else {
       # not a valid number
   }
}