An alternative solution, as pointed out by Stephen in the comments, is to use fileparts with cd (or pwd) to get the directory above the current. It might be useful depending on the context, as it was for me (R2016a) and seems to be for Cecilia, so here it is.
parentDirectory = fileparts(cd);
If you intend to use the saved string in a different platform, make sure the path delimiters are consistent with the platform. Specifically, you will have trouble from Windows to Unix or Mac systems because on Windows fileparts adopts backslashes by default. The other way around is fine because on Windows you can use either forward (/) or back (\) slashes as path delimiters, according to the fileparts documentation.