tl;dr
# qlmanage -t -o <output dir> -s <size> <SVG file>
qlmanage -t -o . -s 640 example.svg
It’s useful to add it as alias command.
# add alias to bash_profile
echo "alias svg2png='qlmanage -t -o . -s '" >> $HOME/.bash_profile
# reload
source $HOME/.bash_profile
# use command
svg2png 640 example.svg
alpha channel(transparency) is not saved in the output png by qlmanage
So white
is used as a background color.