Unintuitive behaviour for uwuw_preproc with flag -o

[helen-brooks]

Currently, the help message flag for uwuw_preproc describes the behaviour for the flag -o as:
-o [--output] : Specify the output filename (default )
I would normally expect an output file specified by command line to be a new file created by the running the executable. While a new file will be created if one is not already present, it will not contain the mesh geometry, only the metadata. The actual intended usage of the flag, which was not immediately clear, is that the output file already exists and contains the same geometry as the input file provided, and the program is simply appending the metadata. In this sense, in my mind this is just another input file (it just happens to be modified).

I would suggest that
i) The help message is improved to reflect the intended usage.
ii) If the output file is being created, the mesh data is then added, or alternatively the program exits with a failure and/or appropriate warning message that the file doesn't exist.
iii) If the program detects that a file does already exist and is just being appended, there should be a warning to the user that it their prerogative to ensure that the geometry is the same. (I could easily envisage a scenario where the wrong file was appended).
iv) Optionally split cases (ii) and (iii) into having separate flags; perhaps -c for create and -a for append, and remove -o entirely due to its ambiguity?
v) Presumably tests should be added for the append/create cases.