G'day Marshall,

++haj already pointed me to a portable solution, using devnull() from File::Spec, which I incorporated into my code.

...
use File::Spec ();
...
    open $null_fh, '>', File::Spec::->devnull();
...
[download]

While writing my original code, I had used state variables so that the "# Increase multiplier for benchmarking" (from NetWallah's OP) would only be called once for each of the multitude of calls by Benchmark::cmpthese(). Unfortunately, subsequently adding code (prior to posting) to test each of the subroutines to be benchmarked ("say 'Test', ...") caused major problems. I didn't spot that until after I posted: I pretty much rewrote the code to fix these problems and added Updates to explain what I'd done.

In order to avoid invalidating what haj had written (as per "How do I change/delete my post?") I left "CAVEAT for MSWin users: ..." but immediately followed it with "Update: ... CAVEAT is no longer valid ..."

I appreciate this ended up all a bit messy. My apologies if it caused confusion.