A few other notes. On Windows it is up to the shell, or application running the program, to get the file extension association from the registry - the OS does not do it (see Win32::FetchCommand).
You can get a list of file extension associations on the command-line with:

assoc|more
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You should see: .pl=Perl. Perl is associated with the perl executable in the registry as well (HKEY_CLASSES_ROOT)
You can create a new association on the command-line with (for example):

assoc .ppl=Perl
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The effect is saved in the registry.