my $text = 12345678.9;

commify($text);

print "\n |$text|\n";

# after Perl Cookbook recipe 2.17
sub commify {
     my $text = reverse $text;
     $text =~ s/(\d\d\d)(?=\d)(?!\d*\.)/$1,/g;
     print "In the sub: " . reverse $text . "\n";
}