#!/usr/bin/perl

use strict;
use warnings;

my $liste;
my $nr;

for (<DATA>) {/^(.*): (.*)$/; push @{$liste->{$1}}, $2;}

foreach my $kuenstler (keys %$liste) {
   print ++$nr,      
         ') ',       
         $kuenstler, 
         "\n\t",     
         join("\n\t", @{$liste->{$kuenstler}}), 
         "\n";
}

_ _DATA_ _
Madonna: Like a Prayer
Madonna: American Pie
Madonna: Frozen
Michael Jackson: Thriller
Michael Jackson: Bad
Michael Jackson: Billie Jean