runcommand/tprocess is not a shell. So you can not expect it to act as such.
You do expect that with your code as it uses a chained command and backticks.
Instead invoke bash and add parameters accordingly. That is a shell that should be capable of handling such things.
More on executing external command can be found
here.
PS: if all you want is a directory listing why not use:
runcommand('ls',[],ss);