First of all, you don't need the './' before your file. @INC should contain your current directory. (this is an array that contains all of the places where perl expects to find code.)
Secondly, name the file Library.pm not Library.pl.
Thirdly, if you are going to reuse this library you might want to use package instead of require. Then you can use $Library::variable to reference the variable in your library and it is perfectly safe for you to reuse variable names in your code without messing with the Library namespace.
happy variable calling from Library!