#!/usr/bin/perl
use strict;
use warnings;

my @array = qw(
    xx1111y000 xx1111y001 xx1111y002 xx2222y000 xx2222y001
);

my %hash;
for my $element ( @array ) {
    if ( $element =~ m/(\w{6})(\w{4})/ ) {
        # fuelle Hash-of-Array
        push @{ $hash{$1} }, $2;
    }
}


for my $key ( sort keys %hash ) {

    # dereferenziere Hash-of-Array und baue String zusammen
    my $value = join ', ', @{ $hash{$key} };

    print qq{<li><a href="$key">$value</a></li>\n},
}

__END__