dget (utility to download debian sources)

dget is part of Debian package called "devscripts" and is a tool to
get debian binary packages or sources in CLI mode.

For simple usage: dget -x -u DEBIAN|UBUNTU_URL/package.dsc, like:

$ dget -x -u http://http.debian.net/../../../../../devscripts_2.15.9.dsc

The sources and patches will download and extracted on current location.

NOTE: On Debian systems dget also can build packages.