#!/usr/bin/perl
use strict;
use warnings;

my $file = $ARGV[0] || 'foo.txt';

open(my $fh, '<', $file) or die "Unable to open '$file' for reading: $!";

my $buffer = '';
while (<$fh>) {
    if (/^\S+domain\.com$/) {
        process_buffer($buffer);
        $buffer = $_;
        next;
    }
    $buffer .= $_;
}

sub process_buffer {
    my ($section) = @_;
    print "================BLAH================\n$section\n";
}