The modernized way of doing this is:
curl -sL https://github.com/user-or-org/repo/archive/sha1-or-ref.tar.gz | tar xz
Replace user-or-org, repo, and sha1-or-ref accordingly.
If you want a zip file instead of a tarball, specify .zip instead of .tar.gz suffix.
You can also retrieve the archive of a private repo, by specifying -u token:x-oauth-basic option to curl. Replace token with a personal access token.