Piping input into Plink in Windows batch file adds extra line feeds

I'm trying to write a batch file to run in Windows 10 Pro that will use Plink to establish an SSH session to a remote server and execute some commands. Everything works well, except for whatever reason I end up with extra line feeds with each ECHO command I pipe in. Normally, this isn't an issue, until the command I'm running requires some specific user feedback, namely, pressing Y to confirm an action. Since it receives the extra line feed after testing STSTest command and before receiving the Y character, it throws an error.

Here's my batch script:

set PATH=C:\Program Files\PuTTY;%PATH%
set TestNum=%1

(
    TIMEOUT /t 1 > nul
    ECHO cd /usr/bin/core/test
    ECHO rm STS_*.txt
    ECHO rm STS_T1_Test%TestNum%.txt
    ECHO ./STSTest --T 2 --i %TestNum%
    TIMEOUT /t 1 > nul
    ECHO Y
    TIMEOUT /t 1 > nul
    ECHO exit
) | plink -ssh 192.168.1.20 -l root -pw ***

Does anybody have an idea on how to eliminate that extra line feed so that Y is entered in the correct order after the STSTest command is entered?

Here's a simpler example demonstrating what I'm fighting. If I define this simple batch file:

(
    TIMEOUT /t 1 > nul
    ECHO cd /
    ECHO cd usr
    ECHO cd bin
    ECHO cd core
    ECHO cd test
    TIMEOUT /t 1 > nul
    ECHO exit
) | plink -ssh 192.168.1.20 -l root -pw ***

The results from the command window look like:

Last login: Wed Jul 29 23:53:30 2020 from 192.168.1.7
root@core-A:~# cd /
root@core-A:/#
root@core-A:/# cd usr
root@core-A:/usr#
root@core-A:/usr# cd bin
root@core-A:/usr/bin#
root@core-A:/usr/bin# cd core
root@core-A:/usr/bin/core#
root@core-A:/usr/bin/core# cd test
root@core-A:/usr/bin/core/test#
root@core-A:/usr/bin/core/test# exit

I get an extra line feed after every ECHO command.

Solution

When you are executing plink without any command on its command-line, plink starts an interactive terminal session. That has lot of unwanted side effects. Including those that you face.

Add -T switch to plink command line to avoid that:

(
...
) | plink -T -ssh 192.168.1.20 -l root -pw ***

Another option is doing everything on the server-side and specifying full command on the plink commandline (in this case, you will also need to add the -batch switch):

plink -ssh 192.168.1.20 -l root -pw *** -batch "cd /usr/bin/core/test && rm STS_*.txt && rm STS_T1_Test%TestNum%.txt && (echo Y | ./STSTest --T 2 --i %TestNum%)"

Or some combination of both these methods.