Hm. Now I get this:

utf8 "\xFF" does not map to Unicode at C:\bin\hexdump.cmd line 40, <> chunk 2.

Any suggestions?

Update: This isn't caused by your sggestion, it happens whenever I pass the filename as a parameter rather than redirecting, though. Looks like another symptom of the same original problem.

Update: I have fixed it by removing the use open ':utf8'; that I had added previously!

Update: ARGH! Now it doesn't work for redirected input! That's OK, though, I can test for parameters before calling perl.