mogrify --version (return code: 0)
Version: ImageMagick 6.8.9-9 Q16 x86_64 2017-02-22 http://www.imagemagick.org
Copyright: Copyright (C) 1999-2014 ImageMagick Studio LLC
Features: DPC Modules OpenMP
Delegates: bzlib cairo djvu fftw fontconfig freetype jbig jng jpeg lcms lqr ltdl lzma openexr pangocairo png rsvg tiff wmf x xml zlib
mogrify -HELP (return code: 1)
mogrify: unable to open image `--help': No such file or directory @ error/blob.c/OpenBlob/2712.
mogrify: no decode delegate for this image format `' @ error/constitute.c/ReadImage/501.