I'll need to determine what they are supposed to be.

I don't think they have to be set to anything. The idea presumably is that in case they are set they should be appended to whatever CCFLAGS / LDDLFLAGS options have been determined via %Config...

IMHO, the code should either test if those vars are defined before interpolating them, or disable warnings :)

As for your update:

from what I can tell, every ENV variable is assigned something, Why are there still 3 concatenation errors?

If you set them within the Perl source, you'll need to set them in a BEGIN { } block, because due to the use Inine (...) statement, they're being evaluated at compile time of the Perl code. 

...
BEGIN {
  $ENV{CFLAGS} = '';
  $ENV{CPPFLAGS} = '';
  $ENV{LDFLAGS} = '';
}
use Inline (
        ...
        ... 
    );
...

[download]

In reply to Re^5: Device::USB gives "Use of uninitialized value in concatenation" error by Eliya
in thread Device::USB gives "Use of uninitialized value in concatenation" error by holandes777

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