According to the documentation on genpath (type help genpath or doc genpath in the Command Window for details)
P = genpath(D) returns a path string starting in D, plus, recursively,
all the subdirectories of D, including empty subdirectories.
So your above result, /Users/myname/:/Users/myname/.Trash:/Users/myname/.Trash/Rec…, includes the path string starting in /Users/myname/, and all subdirectories of * /Users/myname/ with each subdirectory separated by a colon.
As for addpath, in the Command Window type help add path or doc add path for details. It includes several examples
Examples
addpath c:\matlab\work
addpath /home/user/matlab
addpath /home/user/matlab:/home/user/matlab/test:
addpath /home/user/matlab /home/user/matlab/test
I tried addpath(genpath('/Users/geoff/Dev/test')) and it worked fine, adding this directory and all subdirectories as expected. If you are finding that your statement addpath(genpath('/Users/myname')) does not work, then simply edit out the directories from genpath that are invalid:
pathString =genpath('/Users/myname');
% do your edits on pathString
addpath(pathStringEdited);
