Commifying sensibly

Recently, I was thinking about that example in the docs where they demonstrate a method for inserting commas into a numerical string. Now, I realize that they're trying to illustrate a specific mechanism with regexes... but that thing is just clumsy and awful and obfuscated for any Perl beginner. So, just for my own entertainment, I decided to see how I'd do it "for real" - i.e., in the best way possible rather than by this contrived method.

Herewith, humbly, I present a couple of options. :)

#!/usr/bin/perl -w
use strict;

die "Usage: ", $0 =~ /([^\/]+)$/, " <numeric_string>\n"
    unless @ARGV && $ARGV[0] =~ /^\d+$/;
my ($c, @list);
for (reverse split //, $ARGV[0]){
    unshift @list, $c++ % 3 || $c == 1 ? $_ : "$_,";
}
print @list;

# Or, instead of "cheating" with an unquoted list, we could
# aggregate to a string. It's not quite as neat, though. :(
#
# my ($c, $out);
# for (reverse split //, $ARGV[0]){
#     $out = $c++ % 3 || $c == 1 ? "$_$out" : "$_,$out";
# }
# print "$out\n";
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