This is a little cleaner, but I would recommend not reinventing the wheel. Nagios is an excellent system monitoring product.

#!/usr/local/bin/perl
use strict;
use warnings;
use IO::Socket::INET;

my %config = (
              'mail.test.com' => [ 'smtp','pop3' ],
              'localhost'      => [ 'http','dns' ]
              );

my %check;


foreach my $host (keys %config) {
    foreach my $port (@{$config{$host}}) {
        my $host_port = "$host".'_'."_$port";
        $check{$host_port} = IO::Socket::INET->new(
                                                   Timeout  => 1,
                                                   PeerAddr => $host,
                                                   PeerPort => $port,
                                                   Proto    => 'tcp');
    }
}

foreach my $check_it (keys %check) {
    if ($check{$check_it}) {
        print "$check_it is ok\n";
    }
}
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