Using addlistener function - how to output values from event handler?

I would like to write a script that looks for changes to a text file and saves the values recorded in the text file to the workspace.

I am following the example ('Monitor Changes to a .TXT File') on this page: https://uk.mathworks.com/help/matlab/matlab_external/use-net-events-in-matlab.html.

I am able to monitor my text file and print the change in text, however I am stuck on how I can pass the values to the workspace.

If I use the code given in the example, my code looks like the following scripts and I have highlighted what I am would like to do in the comment lines. In this example, I would like to know how I must modify the code, so that the values, x, y and z, found in the 'eventhandlerChanged' function are output in such a way that they will be accessable from the main script.

I appreciate any help you can offer with this.

% Main script that looks for changes in the text file, 'text_file.txt' and
% calls the function 'eventhandlerChanged' upon registering a change
file = System.IO.FileSystemWatcher('c:\work\temp');
file.Filter = 'text_file.txt';
file.EnableRaisingEvents = true;
addlistener(file,'Changed',@eventhandlerChanged);

% ---------------------------------------------------------------
% I would like to be able to output the variables x,y,z from
% eventhandlerChanged, to use here, e.g.
total = x + y + z;
% ---------------------------------------------------------------

function eventhandlerChanged(source,arg)

% Open and read text file
f_ID = fopen('c:\work\temp\text_file.txt','r');
txt_str = fscanf(f_ID,'%s');

% Text file contains a single line with format:
% 'x_value:y_value:z_value
% Split the string at the colons
x_y_z = strsplit(txt_str,':');

% ---------------------------------------------------------------
% These are the variables I would like to pass to the workspace:
x = str2double(x_y_z(1));
y = str2double(x_y_z(3));
z = str2double(x_y_z(5));
% ---------------------------------------------------------------

end

Answer 1

[Jan]

function eventhandlerChanged(source,arg)
% Open and read text file
[f_ID, msg] = fopen('c:\work\temp\text_file.txt','r');
assert(f_ID > 0, 'Cannot open file: %s', msg)
txt_str = fscanf(f_ID,'%s');
fclose(f_ID);  % Important! The operating system can open only a
% certain number of files simultaneously. So after a while, Matlab
% would stuck.

data = sscanf(txt_str, '%f:%f:%f');
assignin('base', 'x', data(1));
assignin('base', 'y', data(2));
assignin('base', 'z', data(3));
disp('::: Values updated :::');  % Do not make this silently
end

The method is fragile: What happens if "file" is overwritten oder cleared? Avoid scripts. Prefer to store a FileSystemWatcher as a persistent variable inside a function.

By the way, "file" is not a good choice for a "System.IO.FileSystemWatcher".

[Fiona N]

Thanks very much for your help and also the extra tips - exactly what I was looking for!