gnmmanage --version (return code: 0)
GDAL 2.2.1, released 2017/06/23
gnmmanage --help (return code: 1)
Usage: gnmmanage [--help][-q][-quiet][--long-usage]
[info]
[create [-f format_name] [-t_srs srs_name] [-dsco NAME=VALUE]... ]
[import src_dataset_name] [-l layer_name]
[connect gfid_src gfid_tgt gfid_con [-c cost] [-ic inv_cost] [-dir dir]]
[disconnect gfid_src gfid_tgt gfid_con]
[rule rule_str]
[autoconnect tolerance]
[delete]
[change [-bl gfid][-unbl gfid][-unblall]]
gnm_name [layer [layer ...]]
Note: gnmmanage --long-usage for full help.