use warnings;
use strict;

my @numb3rs = qw/1024 16777215 3,1415926 42 759092417205229390873,8763617/;

for my $num ( @numb3rs ) {
    print "number: $num\n";
    my $regexed = $num;
    $regexed =~ s/(^[-+]?\d+?(?=(?>(?:\d{3})+)(?!\d))|\G\d{3}(?=\d))/$1./g;
    print "perlfaq: $regexed\n";
    $regexed = $num;
    $regexed =~ s/(\d+)(\d{3})/$1.$2/;
    print "strat:   $regexed\n";
    $regexed = $num;
    $regexed =~ s/(\d\d\d)(?=\d)(?!\d*,)/$1./g;
    print "crian:   $regexed\n";
} continue {
    print '=' x 75, "\n"
}