Just want to thank you all for your help! I got it working, and the code I used is below. Unfortunately, I don't think it is the best way to do it, but it does work. 
#!/usr/bin/perl
use strict;
use warnings;
use Getopt::Long;
use Pod::Usage;

my %alias_hash;
my %host_hash;
my %host_contents;
my %seen;
my $host_id;
my $file1;
my $file2;

GetOptions(
     'h|help'       =>      sub { pod2usage( { -verbose => 1, -input =
+> \*DATA, } ); exit; },
     'm|man'        =>      sub { pod2usage( { -verbose => 2, -input =
+> \*DATA, } ); exit; },
     'f1|file1=s'   =>      \$file1,
     'f2|file2=s'   =>      \$file2,
);
pod2usage( -verbose => 1 ) unless $file1 and $file2;

open(my $file1_handle, '<', $file1) or die "Could not open $file1 ($!)
+\n";
while (my $line=<$file1_handle>) {
    chomp $line;
    if ($line =~ /host id="(.*?)"/)
    {
        $host_id = $1;
    }
    if ($line =~ m{<host-alias>(www.*?)</host-alias>})
    {
        $alias_hash{$host_id}{$1} = -1;         
    }
    if (!$seen{$host_id}) {
        $host_hash{$host_id} = -1;
    }
    $seen{$host_id} = 1;
}
close $file1_handle;
%seen=();

open(my $file2_handle, '<', $file2) or die "Could not open $file2 ($!)
+\n";
while (my $line=<$file2_handle>) {
    chomp $line;
    if ($line =~ /host id="(.*?)"/)
    {
        $host_id = $1;
    }
    if ($line =~ m{<host-alias>(www.*?)</host-alias>})
    {
        $alias_hash{$host_id}{$1}++;  
    }
    if (!$seen{$host_id}) {
        $host_hash{$host_id}++;
    }
    $seen{$host_id} = 1;
}
close $file1_handle;

for my $k1 ( keys %alias_hash ) {
    for my $k2 ( keys %{ $alias_hash{$k1} } ) {
         print "$k2 exists in only $file1\n" if $alias_hash{$k1}{$k2} 
+== -1;
         print "$k2 exists in only $file2\n" if $alias_hash{$k1}{$k2} 
+== 1;
    }
}
while ( my ($key, $value) = each(%host_hash) ) {
    print "$key exists in only $file1\n" if $host_hash{$key} == -1;
    print "$key exists in only $file2\n" if $host_hash{$key} == 1;
}

[download]
P.S.: You may notice that I use Pod::Usage and have not put anything in there for DATA. I just haven't gotten around to it yet, but it doesn't impact this script from working in any way ;)

In reply to Re: Comparing Two Files by walkingthecow
in thread Comparing Two Files by walkingthecow

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