use strict;
use warnings;

our $hosts={};
$hosts->{hosta}->{ip}=192.168.1.1;
$hosts->{hostb}->{ip}=192.168.1.2;
$hosts->{hostc}->{ip}=192.168.1.3;
our $services={};
$services->{1}->{ID}=1;
$services->{1}->{name}='servicea';
$services->{1}->{startup}=sub { print "--> start service 1\n" };
$services->{2}->{ID}=2;
$services->{2}->{name}='serviceb';
$services->{2}->{startup}=sub { print "--> start service 2\n" };

$hosts->{hosta}->{services}->{1}=$services->{1};
$hosts->{hostb}->{services}->{1}=$services->{1};
$hosts->{hostc}->{services}->{2}=$services->{2};

print "--> type hostname\n";
my $host=<STDIN>;
chomp($host);
die "host unknown " unless exists $hosts->{$host};

print "--> which service do you want to use? (Type ID)\n";
while (my ($ID, $service) = each %{$hosts->{$host}->{services}}) 
{
   print "- ID $ID, name ".$service->{name}."\n";
}	
my $ID=<STDIN>;
chomp($ID);
die "service unknown " 
    unless exists $hosts->{$host}->{services}->{$ID};
&{$hosts->{$host}->{services}->{$ID}->{startup}};
exit;

---> output:
--> type hostname
hosta
--> which service do you want to use? (Type ID)
- ID 1, name servicea
1
--> start service 1