I cannot imagine what you would hope to accomplish using an open statement like this:

open PIPE, "pfrrzt >/dev/null |" or die "failed!";
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Given that the command's stdout is being redirected (whether to /dev/null or any other file), nothing would be left for delivery to the pipe. Were you expecting perl DWIMery to do something "coherent" in this case?

I think if there were an executable command called "pfrrzt" in your PATH, the results would still not be what you were hoping for.