Surname L20, First Name L20, Town L20 
-------------------------------------------------- 
Chaplin      Charlie         Basel 
Estevez      Emilio Santa    Manica 
Sarte        Jean Paul       Montmarte 
Rikard       Frank           Amsterdam 
Rodin        Paul            Montmarte 

##</code><code>##

Town         Surname       Firstname

Basel        Chaplin       Charlie          
Manica       Estevez       Emilio Santa   
Montmarte    Sarte         Jean Paul  
Montmarte    Rodin         Paul 
Amsterdam    Rikard        Frank           

##</code><code>##

my $data = "clients.dat";
open (DAT, $data) or die "\"$data\" not existed or can't be opened!\n"
+;
my @client;  # make this an array, not a hash;
my @fields = qw/surname firstname town/;

while (<DAT>) {
    next if ( /^Surname/ or /^-/ );
    my @values = unpack 'A20A20A20', $_;
    my %entry = map { $fields[$_] => $values[$_] } ( 0..$#fields );
    push @client, \%entry;
}

my @towns;
my $client;
foreach my $client (@client){
    push @towns, "$client->{'town'}";
}
my @sorted_towns = sort @towns;

foreach my $key (@sorted_towns) {
    my @elems = $key;
    my $client = $client->[$elems[1]-1];
    print "$client->{'town'} $client->{'surname'} $client->{'firstname'}";
    
}

#Print out the surname of people live in the town
print "Please enter a town name: ";
my $a = <STDIN>;
my $town;
if ($a =~ /[Basel Manica Montmarte Amsterdam]/) {
	       my $client->{'town'} = $a;
                 print ${$client}[$town]
} 

else{
	    die "Invalid town name supplied: $a";
}