Is there a GNU/Linux command line tool that allows to generate an image file from OSM, preferably as an SVG?
Here's a dedicated page for OSM SVG exporting: http://wiki.openstreetmap.org/wiki/SVG
One way to do this through command line would be to use Maperitive - here's a tutorial on how to generate SVG. You can simply write all the commands mentioned in the tutorial into a text file and run Maperitive with the file specified in the command line. Here are some user-written instructions on how to install Maperitive on Linux.
(Disclaimer: I'm the author of Maperitive).
A Perl script called Geo-OSM-Tiles-0.02 might just do the job. From the module's description:
Output's PNGs though.