shell - convert txt file with mixed spaces/tabs to tabs only (where possible) -

I have some source code files that have mixed tabs / spaces and I would like to convert it to a file where it's automatic All indentation spaces by tab for the length of any tab space (for example, tab = 2 spaces) has been replaced by the form.

Any easy solution (with normal Unix tools, macros, bash or zsh)? Some scripts or python commands either?

Thanks, Albert

OK, none of the given solutions satisfied Not done, so I coded it myself :)

Look here: