This is a new follow-on question from this one. Following the documentation outlined in the answer, it is fairly easy to set up a descriptor text file for standard utilities that exist but aren't in the Processing tool box. I have been testing this with a few official but undescribed utilities.
On restarting QGIS, the new descriptor is recognised and a dialog box will appear as expected. The process will run and, if the Options and Flags are specified in the descriptor as per the utility's manual page, the process will run without any reported error but the output is empty (in one example - r.out.bin). In another example, despite specifying the output file I get an error stating that no output file was specified (r.out.gdal)! This latter error I have noticed in another official utility with an official descriptor (r.out.vrml).
So, are there just some GRASS utilities that cannot run via QGIS, or am I doing something fundamentally wrong (if it's the latter then I don't understand why the official descriptors sometimes seem 'broken')? I am using QGIS 2.18 and have tested with both GRASS 6.4.3 and 7.2 on Windows 10 (64 bit).
Here is my descriptor for r.out.bin:
r.out.bin Exports GRASS raster map to a binary array Raster (r.*) ParameterRaster|input|input|False ParameterBoolean|-i|Generate integer output|True ParameterBoolean|-f|Generate floating-point output|False ParameterBoolean|-h|Export array with GMT compatible header|False ParameterBoolean|-b|Generate BIL world and header files|True ParameterBoolean|-s|Byte swap output|False ParameterNumber|null|Value to write out for null|None|None|0 ParameterSelection|bytes|Number of bytes per cell|1;2;4;8|0 ParameterSelection|order|Output byte order|big;little;native;swap|2 OutputFile|output|Output
EDIT: After more research, I am beginning to think that r.out.bin itself is broken. I have tested with several different datasets in GRASS 7.2 (standalone - not via QGIS) and r.out.bin consistently returns the same error "Unable to create file ". This is odd as r.out.bin is apparently based on r.out.ascii and that utility works just fine. Can anybody confirm that r.out.bin actually works?
EDIT2: After further testing, r.out.bin does work OK in standalone GRASS if a non-default file name/location is chosen. However, this does not solve the problem when running through QGIS Processing.