Run some bash commands with SSH remotely using local variables

In this example, we want to make sure a certain file exists on the remote server:

file=/tmp/file.log
ssh ${options} ${login} "if [ ! -e '$file' ] ; then touch '$file' ; fi"

Notice the command is surrounded by double quotes, and the $file variable is surrounded by single quotes. That has the effect to be wordsplit-proof in the local shell (due to the double-quotes) and in the remote shell (due to the single-quotes).