dnsupdate was written to use TSIG dns keys. It should be updated to
tolerate shared secrets if that doesn't already happen to work.

dnsupdate tries to be quite intelligent with the defaults, getting
hostname and domainname from the host and updating to the NS server for
domainname as returned by a dns query. As indicated in the '-h' output,
a well configured host will likely only need the key option and nothing
else to make the update.

Depends on dig, nsupdate, curl, as well as some pretty standard unix
stuff (bash, cat, etc)