inkscape command line, where is it on mac?

I have Inkscape installed in /Applications and running this from a terminal does the trick:

/Applications/Inkscape.app/Contents/MacOS/inkscape --help

Usage: inkscape-bin [OPTIONS...] [FILE...]

Available options:
  -V, --version                             Print the Inkscape version number

... etc.

For ease of use symlink it to /usr/local/bin i.e.:

ln -s /Applications/Inkscape.app/Contents/MacOS/inkscape \
      /usr/local/bin/inkscape

In general, on MacOS Inkscape needs to be called with an absolute path, and all files given as arguments should also be full paths. See also:

https://bugs.launchpad.net/inkscape/+bug/1449251

As of 2020, the executable on MacOS is now located at

/Applications/Inkscape.app/Contents/MacOS/inkscape

You can symlink it with:

ln -s /Applications/Inkscape.app/Contents/MacOS/inkscape \
  /usr/local/bin/inkscape

More info about command line usage here.