Here is a example where I am retreiving the first matched group or token.

string = 'adcout1_TAG_i.txt';
[tok] = regexp(string, '([^_]+).*[iq]\..*', 'tokens');
datapath_point = char(tok{1}); % convert cell to string
% returns 'adcout1' (without quotes)

Note that ’tokens’ argument to the Matlab regexp function makes that function return a cell of tokens. In the above example that is stored in tok cell. In order to use that cell element as a string, I need to first convert it to a string using the char function.