Your code doesn't make a great deal of sense to me. In particular I can't see why you are interpolating $HN into the regex. However the following sample does what you ask and should serve as a starting point for you to ask what you really want to know: 

use strict;
use warnings;

while (<DATA>) {
    next if ! /^((?:\d{1,3}\.){3}\d{1,3})\s+(\S*)/;
    print "$1\n";
    print "$2\n";
}

__DATA__
0.0.0.22    fred localhost
0.0.63.23    fred-test-0
1.0.128.24    fred-test-1

[download]

Prints:

0.0.0.22
fred
0.0.63.23
fred-test-0
1.0.128.24
fred-test-1

[download]

Note the use of \d{1,3} to match 1 to 3 digits and \s and \S to match white space and anything else respectively.

DWIM is Perl's answer to Gödel

In reply to Re: Passing variables into regular expressions by GrandFather
in thread Passing variables into regular expressions by wanderer

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.