require checks %INC to see if a file has already been loaded. This is explained in the documentation.

use also checks %INC (because it is exactly equivalent to BEGIN { require Module; Module->import( LIST ); }) but regardless of whether the module was already loaded or not it still calls the import() method.

In reply to Re: Why do multiple requires not work? by DrHyde
in thread Why do multiple requires not work? by srinigs

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