Why not portable? Why source filters? I sure it as simple as: 
eval q{*O_NONBLOCK = \\}.O_NONBLOCK;

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This code work, and work even a little (1-20%) faster than usual scalar! It's portable and can be executed automatically in import() if it see user try to import $O_NONBLOCK instead of O_NONBLOCK.

In reply to Re^2: Import constants as scalar instead of bareword sub by powerman
in thread Import constants as scalar instead of bareword sub by powerman

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