How to read error output stream in batch file?

Question

I have a batch script that starts a server. This server then prints out its logs to the STDOUT and STDERR in case of errors.

I want to redirect both STDOUT and STDERR to a tee command to split the output. Using the tee command from UnxUtils this worked just fine.

However in order to make my application portable I cannot depend on UnxUtils so I need to write my own tee command.

I wrote a batch script that reads out the STDOUT like suggested in this answer (2. codeblock).

This works, but only for the redirected STDOUT and not for the STDERR.

Note: Output from STDERR is missing in both the file and the command line.

How can I make it read both streams?

How I redirect the output (%1 is the server, %2 is the file I want the logs to go to)?

%1 2>&1 | %~dp0tee.bat -a %2

This works fine (as it calls UnxUtils, not my batch script):

%1 2>&1 | tee -a %2

How I read the input in tee.bat:

for /F "tokens=*" %%a in ('findstr /n $') do (
    set "line=%%a"
    setlocal EnableDelayedExpansion
    set "line=!line:*:=!"

    echo(!line!

    if %append%==true (
        echo(!line! >> %output%
    ) else (
        echo(!line! > %output%
    )
    endlocal
)

Your answer is on this page stackoverflow.com/questions/41030190/command-to-run-a-bat-file/… — Noodles
– Noodles, Commented May 2, 2019 at 21:33

lit · Accepted Answer · 2019-05-02 23:45:42Z

1

PowerShell has a Tee-Object cmdlet. The $Input variable receives stdin.

echo asf 2>&1 | powershell -NoLogo -NoProfile -Command "$Input | Tee-Object -FilePath './tee.txt'"

See also: https://stackoverflow.com/a/38668360/447901

edited May 2, 2019 at 23:45

answered May 2, 2019 at 23:39

lit

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1 Comment

Lahzey Over a year ago

I knew PowerShell had that command, however I did not know you could use it while still printing the output in the classic cmd. Thanks alot!

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