Thank you for your response.
The modules I used today have something bad. I thought It was because the names of the module and the name of the file are not aligned.
When I use them from a command line script, everything works fine.
But if I use them within a Dancer's (the CPAN module "Dancer") application… it is a big mess. Many variables "become" suddenly undefined…
Note : these modules have been written in a hurry by some developers that don't respect good pratices (no "use strict", no naming conventions for variables or functions…).
So I use these modules through "system()" (that is, in a totally separated environment)… It's really bad, but, at least, it works…
Well, it is something else. I'll try to find out if I have some time.