Is there a free command line program for converting PDF files to SVG?
Turns out Inkscape has a command line mode. I added this to .bash_profile:

alias inkscape="/Applications/Inkscape.app/Contents/Resources/bin/inkscape"


and now this command converts from PDF to SVG:

inkscape Logo.pdf --export-plain-svg=Logo.svg


Unfortunately, the current version of Sketch has very rudimentary SVG import capabilities and can't correctly read any of the files I've made even though they display fine in Opera and OmniWeb. The company says future versions will do better.