Welcome to the forum!
I think there is a portable version of Inkscape. One might guess that it might be somehow smaller, but I don't think it's any different from the regular version. As far as I know, you have to install the full version. It's the only version, as far as what it contains (although different versions for Windows, Linux and Mac, 32 bit and 64 bit, and portable, as mentioned.
If you knew enough about it, you might be able to build some kind of custom version which only works from the command line. I could be wrong, but I don't think what you're looking for exists. You can find everything either on this page or linked to it:
https://inkscape.org/en/download/Edit
Although I imagine a commandline only version might be attractive for a lot of people. If you wanted to get a little more involved, you could write a feauture request. Or maybe there already is a request? You could search here:
https://launchpad.net/inkscape. And if you don't find it already requested, you could make the new report.
