#!/bin/sh
REMOTEMD5=$(ssh user@host 'md5sum file.txt')
LOCALMD5=$(md5sum 'file.txt')
if [ "$LOCALMD5" == "$REMOTEMD5" ]
then
echo "all OK"
else
echo -e "no match, Local:"$LOCALMD5"\nRemote:"$REMOTEMD5
fi
The space between the bracket and the value is important!