[PHP] include problem

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Hi

I have a little Problem with include.I want to include a txt file in every php file on 
the server but some php files are in other directories and dont include this txt file.

Example :

Url for the txt file : www.domain.com/include/incl.txt

So www.domain.com/index2.php includes the txt file correctly but 
www.domain.com/shop/shop.php dont do this.

In the include command i used the serverpath to the txt file.

So what should i do ?
Thanks for support !

chris