mkgrkindex version (return code: 0)
This is mkgrkindex (previously known as mkindex) version 2.2
This is makeindex, version 2.15 [TeX Live 2017] (kpathsea + Thai support).
Scanning input file version...done (0 entries accepted, 1 rejected).
Nothing written in version.ind.
Transcript written in version.ilg.
mkgrkindex --help (return code: 0)
This is mkgrkindex (previously known as mkindex) version 2.2
Unknown option --.
Usage: makeindex [-ilqrcgLT] [-s sty] [-o ind] [-t log] [-p num] [idx0 idx1 ...]