#!/usr/bin/perl

use strict;
use warnings;

my $liste;

while (<DATA>) {
    chomp $_;
    my ($kuenstler, $titel) = split /\: /, $_;
    push @{$liste->{$kuenstler}}, $titel;
}

my $nr = 0;

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

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