Q: Lemonldap skin rule based on url parameter I try to configure lemonldap to use different skin based on the url.
I use this documentation :
http://lemonldap-ng.org/documentation/1.9/portalcustom
It says:

Rule: a Perl expression (you can use %ENV hash to get environment variables, or $_url to get URL called before redirection, or $ipAddr to use user IP address). If the rule evaluation is true, the corresponding skin is applied.

I try to write a rule that return true if the $_url contains a parameter. But I don't know Perl language.
For example, if the url is http://myurl:8097/?skin=dark, I want to use the dark skin. If the url is http://myurl:8097/?skin=pastel, I want to use the pastel skin. 
How can I check this with a perl expression?
I already try:
$_url =~ dark

$_url =~ $dark

$_url =~ /dark

None of this works.

A: You're looking for
$_url =~ /dark/

The match operator is documented in perlop. (Search for the bullet starting with m/PATTERN/.)
It's a poor check since it looks for dark anywhere in the URL. The following would be better:
$_url =~ /[?&;]skin=dark(?:[&;]|\z)/

