my $major_div = '!!';
my $user_div = ';';
my $var_div = ',';
my $full_string = 'abcd-efgh-ijkl-mnop;key1=data1,key2=data2;key1=data3,key2=data4!!qwer-asdf-zxcv-tyui;key1=data3;key3=data6!!trew-hgfd-ytre-bvcx;key1=data7,key2=data8;key1=data9,key2=data10!!erty-dfgh-cvbn-hjkl;key2=data5;key3=data6';

sub field_split {
    my ($sep, $field, $source) = @_;
    return (split /\Q$sep/, $source)[ $field-1 ]
};

my $major_field = &field_split($major_div, 3, $full_string);
my $user_key = &field_split($user_div, 1, $major_field);
my $user_vars1 = &field_split($user_div, 2, $major_field);
my $user_vars2 = &field_split($user_div, 3, $major_field);
my $key_data = &field_split($var_div, 1, $user_vars1);