The perlfunc section of docs in your development environment is probably most convenient. In ActiveState those are distributed in a winhelp format and accessable through the AS start menu. On unix just type 'perldoc -f use'. use is like #include in C, but with specific behavior at compile time, and with regard to multiple inclusion.

1. perldoc perlfunc
2. perldoc perlsyn
3. perldoc perlop
4. perldoc IO::File

After Compline,
Zaxo