Any ideas about how to proceed with debugging,

To see what is being received from the pipe, use a one-liner to receive and redirect it: 

perl units.pl COM1 < dmp4.tests > dmp4.results
perl units.pl COM1 < dmp4.tests | perl -pe1 > dmp4.piped

diff dmp4.results dmp4.piped

[download]

Then you can compare the two.

What are those COM1 references doing?

The comments mention warnings and errors. You are only piping/redirecting STDOUT not STDERR? Not that it should make any difference in what gets redirected or piped as STDERR would get displayed on the console in both cases--unless you are redirecting stuff internally to the program? To the serial port for example?

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
Lingua non convalesco, consenesco et abolesco. -- Rule 1 has a caveat! -- Who broke the cabal?
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.

In reply to Re: cmd.exe piping stress by BrowserUk
in thread cmd.exe piping stress by tomazos

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