grep command doesn't work when run remotely

I have a script like this:

if rsh $server grep "string" /usr/path/file.txt
then
   echo "yes"
else
   echo "no"
fi

Basically I want to check the file in remote server containing some specific strings. It doesn't work and always display "yes" whatever I put into "string".

However, if I remove "rsh $server", which means running locally, and put that file into local, it is working fine.

Does anyone know what the problem is? How can I modify my script?

You can run grep locally with data from the remote file:

if rsh $server cat /usr/path/file.txt | grep "string"
then
    echo "yes"
else
    echo "no"
fi

This will be slow if the file is large, since the entire file has to be sent over the network so that the local grep can read it.