curl/wget experience

curl -C - -o --location
"-C -" specifies Resume.
-o specifies the file name to store.
--location specifies the download address. If needed redirect, then follow redirect.

for example,
curl -C - -o bt4-r2-vm.tar.bz2 --location http://www.backtrack-linux.org/download.php?fname=bt4r2vm

wget --continue --trust-server-names http://downloads.raspberrypi.org/raspbian_latest
it will finally stores as 2014-12-24-wheezy-raspbian.zip.