How can I write data to a text file in a user-specified location that is already populated with a standard header?

Currently, I am working on an app that can successfully write 4 columns of data to a text file in a user-defined file location, at the push of a button. I am accomplishing this task using the following code:

% Button pushed function: ExporttotxtButton
        function ExporttotxtButtonPushed(app, event)
   
   [fn,pn] = uiputfile('.rdf','RoadProfile_bumpy_fl.rdf','RoadProfile_bumpy_fl.rdf'); 

if isnumeric(fn) % user canceled
    return       % return early
end
% write the table to the user-specified file
writematrix(app.UITable.Data,fullfile(pn,fn),'Delimiter','tab','FileType','text');

However, I have a very long string of text (about 47 lines of text...not included here to save space) that I would like to include as a header in the generated text file. The goal is to have the end result be a text file that already has the header populated with a standard 47 lines of text, and then write the matrix data below the header as I am already doing. I have tried using the following:

fprintf(fullfile(pn,fn),'%s\n',['long_string_of_text..' ...
    'creating new line each time\n'...]

But, this doesn't seem to work. Any help would be much appreciated. I can post the full text that I want to include in the header if that is necessary. Thank you.

Answer 1

[Voss]

You can call writematrix with 'WriteMode','append' to write the data to a text file that already contains the header.

So the complete file would be built by doing something like:

header = ["some";"lines";"of";"text";"in";"some";"form";"or";"other"];
file_name = fullfile(pn,fn);

% write the header
writematrix(header,file_name,'FileType','text');

% write the data
writematrix(app.UITable.Data,file_name,'Delimiter','tab','FileType','text','WriteMode','append');

Or use writecell or writetable to write the header, depending on its data type, then writematrix(_,'WriteMode','append') the data as above.

[Jack Lebar]

This worked perfectly, thank you!

[Voss]

You're welcome!

Answer 2

[Les Beckham]

Probably the easiest way to do this is to create a text file containing your header text and then call system() to concatenate that file with the one that you have written your data table to.

For example (on Windows):

% insert after your writematrix() call above:
cmd = sprintf('copy HeaderText.txt + %s %s', fullfile(pn,fn), fullfile(pn,fn))
system(cmd)

Or on Linux:

% insert after your writematrix() call above:
cmd = sprintf('cat HeaderText.txt %s > %s', fullfile(pn,fn), fullfile(pn,fn))
system(cmd)

Note that I haven't tested either of these examples, but they should get you started.