Editing large number of dat files

Hello all,

I want to add the same comment to the second line of a large number of dat files and then place them in a new folder.

I was thinking of doing something like this:

    NewFiles = fullfile(pwd, 'NewFiles')

    if exist([pwd '\NewFiles'])~=7   

    mkdir(NewFiles);  

    end

files = dir(fullfile('*.dat')); 

filenames = {files.name};                 

    for i = 1 : length(filenames)

     fid(i) = fopen(files(i),'w');
     fprintf(fid,'try \n');
     fclose(fid);
     dlmwrite(fname,'-append') ; 

    end

This code does not work, obviously.

Any suggestions ?

Thank you