So something like:

use strict;
use warnings;

my $HN = 'fred';

while (<DATA>) {
    next if ! /^((?:\d{1,3}\.){3}\d{1,3})\s+(\S*)/;
    next if $HN ne $2;
    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
[download]

is what you are after? You could do the test in one line or you could interpolate the variable into the regex, but has the advantage of being pretty clean and clear I think.

I wanted to make one suggestion, instead of having a pure Regular Expression break it apart and assign it to variables to make it more readable.

use strict;
use warnings;

my $IP_ADDRESS = qr{(?:\d{1,3}\.){3}\d{1,3}}xms;
my $HOST_NAME  = qr{\S*}xms;

my $HN = 'fred';

while (<DATA>) {
    next if ! qr{\A ($IP_ADDRESS) \s+ ($HOST_NAME) }xms;
    next if $HN ne $2;
    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]