Without wanting to be influenced by the other comments, my opinion is that it's too much, without braces or a comment to make it clear in what order things happen, or why they are happening.

Without the braces I probably have to .. no, I have to look up what the precedence order is, or try it in the debugger. Yes, certainly after developing in Perl for ten years I should probably know that, but I don't. Also, the assignment to $country followed immediately by a re-assignment to $country isn't a style I love.

OK, (after trying it in the debugger) it does do the ternary first and the if statement within that .. that's what I expected.

To answer your question, no, this code is not clear.

Was there a comment explaining the business logic? The left side of my brain suggests ..

  #  Blank country field if Great Britain, otherwise upper
  #  case country name within square brackets. Leave field
  #  empty if country is undefined.
[download]

.. but the right side of my brain prevails, and provides a much better comment:

  #  Since we're mailing from GBR, only display the country
  #  if it's not GBR, and leave a blank country field blank.
[download]

Above all, strive for clarity.