Convert SVG to DXF or DWG via PHP or Command line?

I am trying to find a way to convert a web SVG graphic to DFX or DWG usi开发者_StackOverflowng the server to automate the process. I am trying to avoid downloading the SVG and converting it in a program that a user would have to do.

Does anyone have any experience with this?

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Have you seen this: http://en.wikibooks.org/wiki/OpenSCAD_User_Manual/Other_2D_formats ? The premise works in a terminal, I'm only having issues getting pstoedit to run from PHP's exec(), but it may be a permissions issue. It creates an empty DXF and throws an error with mkstemp. (I'm running on OS X 10.7.1)