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Normally if you try to copy a file that does not exist you get an error message:
C:\temp>copy foo bar
The system cannot find the file specified.
I would expect that error message to be written to STDERR but it appears to be written to STDOUT:
C:\temp>copy foo bar >out
C:\temp>dir
Directory of C:\temp
23/09/2019 16:18 44 out
1 File(s) 44 bytes
0 Dir(s) 885,229,346,816 bytes free
C:\temp>type out
The system cannot find the file specified.
The same apparently happens if you redirect STDERR separately from STDOUT
C:\temp>del out
C:\temp>copy foo bar 2>err >out
C:\temp>dir
Directory of C:\temp
23/09/2019 16:10 0 err
23/09/2019 16:10 44 out
2 File(s) 44 bytes
0 Dir(s) 885,226,635,264 bytes free
C:\temp>type out
The system cannot find the file specified.
I am using Windows 10
C:\temp>ver
Microsoft Windows [Version 10.0.18362.356]
Why does COPY not write error messages to STDERR? Where is this behaviour documented?
RedGrittyBrick
Posted 2019-09-23T15:26:12.533
Reputation: 70 632
This is not execution error. This is parameter error not relative to the copying process, which have not started yet. – Akina – 2019-09-23T15:54:50.213
1
@Akina: It's still an error and as such should go to stderr. In fact, it is exactly the kind of error that stderr was invented for.
– user1686 – 2019-09-23T17:30:36.937@grawity Program author is the only who can decide what problem is error and what is not. But in this particular case
%ERRORLEVEL% = 1- so it is really programmer's mistake. – Akina – 2019-09-23T18:24:22.673