inkscape

TLDR

Open an SVG file in the Inkscape GUI

$ inkscape [filename.svg]

Export an SVG file into a bitmap with the default format (PNG) and the default resolution (96 DPI)

$ inkscape [filename.svg] -o [filename.png]

Export an SVG file into a bitmap of 600x400 pixels (aspect ratio distortion may occur)

$ inkscape [filename.svg] -o [filename.png] -w [600] -h [400]

Export the drawing (bounding box of all objects) of an SVG file into a bitmap

$ inkscape [filename.svg] -o [filename.png] -D

Export a single object, given its ID, into a bitmap

$ inkscape [filename.svg] -i [id] -o [object.png]

Export an SVG document to PDF, converting all texts to paths

$ inkscape [filename.svg] -o [filename.pdf] --export-text-to-path

Duplicate the object with id="path123", rotate the duplicate 90 degrees, save the file, and quit Inkscape

$ inkscape [filename.svg] --select=path123 --verb="[EditDuplicate;ObjectRotate90;FileSave;FileQuit]"