Extracting URIs - rapper --trace?

Hi.
I wanted to extract the URIs from some rdf, and it struck me that rapper probably did it for me.
And yes, that is what the -t/—trace flag says it does, I think.
"       -t, --trace
              Print URIs retrieved during parsing.  Especially useful for monitor-
              ing what the guess and GRDDL parsers are doing.”

But I can’t get it to make any difference - am I doing something wrong, please?
Best
Hugh
-- 
Hugh Glaser
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Received on Sunday, 9 February 2014 18:04:38 UTC