#!/usr/bin/perl --
use strict; use warnings;
use 5.010;
use Data::Dump;
my $re = qr{
(?(DEFINE)
  (?<byte>
    2[0-4]\d
    | 25[0-5]
    | 1\d\d
    | [1-9]?\d
  )
)

# match this
( # save to  $1
  \b
  (?&byte)
  (
    \.
    (?&byte)
  ){3}
  \b
)
}x;

my $str =  ' localhost 127.66.66.66 ';
while( $str =~ m/$re/g ){
    dd( [ $1, \%+, \%-, \%/ ] );#/
}
dd([  $str =~ m/$re/g ] );
use Tie::Hash::NamedCapture;
tie my %hash, "Tie::Hash::NamedCapture", all => 1;
if( $str =~ m/$re/g ){
    dd([ $1, \%hash ]);
}
__END__
[
  undef,
  {
    # tied Tie::Hash::NamedCapture
  },
  {
    # tied Tie::Hash::NamedCapture
    byte => [undef],
  },
  {},
]
[undef, "127.66.66.66", ".66"]
[
  undef,
  {
    # tied Tie::Hash::NamedCapture
    byte => [undef],
  },
]