How to use wintee to redirect STDERR only?

Question

I'm currently using wintee to log the result messages from testing scripts. Here's what the command looks like:

test_name.bat [parameters] 2>&1 | wtee log.txt

However, I only would like to archive STDERR to a file, while still displaying both STDOUT and STDERR to the console. The problem emerges from wintee's limitation: it seems to only fork STDIN, STDOUT, and input files.

Here's what I'm trying to do:

Redirect STDOUT to stream 3 (unused stream)
Redirect STDERR to STDOUT
Redirect stream 3 (the redirected STDOUT) to STDERR

This way, the console will still display both streams' messages, while wintee will only fork the messages from (what originally was) STDERR.

However, I'm not sure whether if it's possible, as my understanding of the stream redirection is shallow. I'm trying to see if I can redirect STDOUT to STDERR using another stream in between:

echo Hello World! 3>&2 >3

However, it isn't printing anything.

Is what I'm trying to accomplish possible in native batch (optionally with helps of other tools)? If so, what am I doing wrong?

score 2 · Answer 1 · edited May 16 '18 at 01:22

2

Set Arg = WScript.Arguments
set WshShell = createObject("Wscript.Shell")
Set Inp = WScript.Stdin
Set Outp = Wscript.Stdout   
On Error Resume Next

Set Fso = CreateObject("Scripting.FileSystemObject")
Set File = Fso.CreateTextFile(Arg(0), True)
If err.number <> 0 then
    Outp.WriteLine "Error: " & err.number & " " & err.description & " from " & err.source
    err.clear
    wscript.exit
End If
Do Until Inp.AtEndOfStream
    Line=Inp.readline
    outp.writeline Line
    File.WriteLine Line
Loop

This Tees StdOut. Changing the 4th line to Set Outp = Wscript.Stderr will make it Tee StdErr.

To use dir | cscript //nologo Tee.vbs.

edited May 16 '18 at 01:22

phuclv

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answered Oct 05 '16 at 21:17

I guess there is the log file missing in the usage string, right? Anyway, if I specify one or not, I am getting error 9 (Subscript out of range); when I change `Arg(1)` to `Arg(0)`, no error arises; can you tell me why this happens? (`Arg(0)` should point to the script itself, and `Arg(1)` to the first argument, true?) – aschipfl Oct 06 '16 at 10:06
Not in VBScript. That is CMD's rules. In VBScript 1st param is arg(0). The [almost] equivalent of %~dp0 is `wscript.ScriptFullName` . – Oct 06 '16 at 11:31
Ah, I see, that explains the error I am getting; thanks... So `Arg(1)` needs to be changed to `Arg(0)` in your script... – aschipfl Oct 06 '16 at 11:33
Yes, it is part of a larger file where Arg(0) is the sub command. So yes change. – Oct 06 '16 at 12:45
The larger file is called filter and is here https://1drv.ms/w/s!AvqkaKIXzvDigWyNPt14cNh-m9Ji – Oct 06 '16 at 21:17

score 0 · Answer 2 · edited May 23 '17 at 12:15

I do not know the wintee command, but I think I can help you with the redirection issue:

Instead of test_name.bat [parameters] 2>&1 | wtee log.txt, you should write the following:

(test_name.bat [parameters] 2>&1 1> con) | wtee log.txt

This writes the text at STDOUT to the console, redirects the data at STDERR to STDOUT, which is in turn passed to the wtee command.

Note that the console displays all original STDOUT before any STDERR data, because the former is displayed immediately, while the latter is passed through wtee. With pure redirection hacks it is not possible to preserve the original order which the data was returned with. ~~If you insist on that, you need to use a tool other than wintee which has got the required capabilities.~~ Edit: In particular, the pipe is the bottleneck, because there is only one channel, namely STDIN, where it passes data to. So if you insist on STDOUT and SRDERR data to be displayed in the original order while saving the data of one stream to a file, you have no other choice but to modify the script test_name.bat and to avoid piping.

I am trying to explain that using the command dir ":" on the left side of the pipe, which produces output at both STDOUT and STDERR (because of the invalid path ":"):

D:\Data> dir ":"
 Volume in drive D has no label.
 Volume Seriel Number is 0000-0000

 Directory of D:\Data

File Not Found

The File Not Found message appears at STDERR, whereas the rest appears at STDOUT (you can prove that by redirecting like 2> nul or 1> nul to dismiss either of the streams).

On the right side of the pipe, I am using the command find /V "", which simply passes all data it receives at STDIN through and displays it on the console:

D:\Data> dir ":" | find /V ""
File Not Found
 Volume in drive D has no label.
 Volume Seriel Number is 0000-0000

 Directory of D:\Data

The changed order of the console output illustrates what happens: STDERR is displayed immediately, whereas STDOUT is first passed through the pipe before being displayed.

Now let us apply the redirection 2>&1 from your command line:

D:\Data> (dir ":" 2>&1) | find /V ""
 Volume in drive D has no label.
 Volume Seriel Number is 0000-0000

 Directory of D:\Data

File Not Found

This redirects STDERR to STDOUT, so the original STDOUT data together with the redirected ones are piped through. Replacing find /V "" by (> nul find /V "") proves that the right side of the pipe really receives all of the data.

Now let us add the 1> con portion, which constitutes an explicit redirection of STDOUT to the console:

D:\Data> (dir ":" 2>&1 1> con) | find /V ""
 Volume in drive D has no label.
 Volume Seriel Number is 0000-0000

 Directory of D:\Data

File Not Found

The output contains all of the original data. Again replacing find /V "" by (> nul find /V "") proves that this time, the right side of the pipe truly only recieves the File Not Found message, which was originally present at STDERR, but the STDOUT data are not piped through.

Just a side-note:
If you want to do something like wintee with pure batch-file, things become very complicated -- see this example...

How to use wintee to redirect STDERR only?

2 Answers2