I am trying to use GRASS on the command line, specifically the `r.thin` module. It seems to execute properly but I have no output raster dataset to work with afterwards, it is as if it just gets swallowed into the void. This is the exact command:

`grass79 -c /data/mapset/PERMANENT --exec r.thin input=dummy_img output=thinned`

And I get the following output:

    Starting GRASS GIS...
    WARNING: Mapset </data/mapset/PERMANENT> already exists. Ignoring the request to create it. Note that this warning may become an error in future versions.
    Cleaning up temporary files...
    Executing <r.thin input=dummy_img output=thinned> ...
    Raster map <dummy_img> - 658 rows X 658 columns
    Execution of <r.thin input=dummy_img output=thinned> finished.
    Cleaning up temporary files...

So it seems that it executed properly.

But when I look inside the /data/mapset/PERMANENT folder, I see only the `dummy_img` (which was already there) and no mention of `thinned`:

```
$ ls data/mapset/PERMANENT
dummy_img
```

Am I doing something wrong? [here](https://grass.osgeo.org/grass76/manuals/r.thin.html) is the docpage but I don't see any specific caveats to this.