gdal_merge.py --version (return code: 0)
GDAL 2.2.1, released 2017/06/23
gdal_merge.py --help (return code: 1)
Unrecognized command option: --help
Usage: gdal_merge.py [-o out_filename] [-of out_format] [-co NAME=VALUE]*
[-ps pixelsize_x pixelsize_y] [-tap] [-separate] [-q] [-v] [-pct]
[-ul_lr ulx uly lrx lry] [-init "value [value...]"]
[-n nodata_value] [-a_nodata output_nodata_value]
[-ot datatype] [-createonly] input_files
[--help-general]