Convert absolute HTML anchors to relative ones for the Kindle

If you've ever tried to save and convert an entry from Wikipedia to the format MOBI for the Kindle, you would find the links of the table of content still point to internet addresses so that the web browser would be invoked to open the specified page on click. This is circuitous! Fortunately, a command-line tool "web2disk" bundled with Calibre does the conversion.

prompt:~$> web2disk -r 0 [-d DIR] http://example.url

You can optionally specify the argument DIR for the base directory to save the downloaded materials. Anyway, the saved web page should have the absolute anchors converted. Subsequently, invoke Calibre to convert it to the desired output format as usual. That's all.