I'll explain in english what I need.

That can be useful but it's fuzzy. Far better to write tests which may or may not work. See How to ask better questions using Test::More and sample data

If you can negate the logic then (from your fuzzy description) I think it should be quite simple:

use strict;
use warnings;

use Test::More;

my @good = qw/PKG_CONFIG_PATH  XDG_DATA_DIRS/;
my @bad = qw/XDG_SEAT_PATH XDG_SESSION_PATH/;

plan tests => @good + @bad;

my $re = qr/^XDG.*PATH$/;

for my $str (@good) {
    unlike $str, $re, "good $str does not match";
}

for my $str (@bad) {
    like $str, $re, "bad $str matches";
}
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