How do I write a MATLAB code that edits another MATLAB file (.m)?

Question

I have two files, Editor.m and Parameters.m. I want to write a code in Editor.m that when run does the following task:

• reads Parameters.m
• searches for a line in it (e.g. dt=1)
• replaces it with something else (e.g. dt=0.6)
• saves Parameters.m.

So, at the end of this process, Parameters.m will contain the line dt=0.6 instead of dt=1, without me having edited it directly.

Is there a way to do this? If so, how?

Answer 1

You can use regexprep to replace the value of interest.

% Read the file contents
fid = fopen('Parameters.m', 'r');
contents = fread(fid, '*char').';
fclose(fid);

% Replace the necessary values
contents = regexprep(contents, '(?<=dt=)\d*\.?\d+', '0.6');

% Save the new string back to the file
fid = fopen('Parameters.m', 'w');
fwrite(fid, contents)
fclose(fid)

If you can guarantee that it will only ever appear as 'dt=1', then you can use strrep instead

contents = strrep(contents, 'dt=1', 'dt=0.6');