While everyone is familiar with bash’s TAB completion for paths and filenames, fewer people know that since bash 2.04, TAB can complete arguments in many more contexts thanks to a feature called programmable bash completion. The default completions handle mount, cvs, ant, ssh and many others; it’s also possible to program your own extensions for whichever command seems to stress your typing.

For me, ssh completion (which completes based on known host names, and consequently learns knew hosts as you ssh into them) has been one of the most useful plug-ins. Unfortunately, it has stopped working a while ago (Ubuntu Breezy to be more precise). I have recently discovered the real cause: as a security feature, ssh hashes host names instead of saving them directly into the known hosts file. This feature is meant to prevent worms from learning host names and spreading to them via ssh — except there aren’t many Linux worms around now or in the foreseeable near future. You can disable hashing by adding

HashKnownHosts no

into /etc/ssh_config, or alternatively, you can list some frequently used hosts into your ~/.ssh_config, e.g.:

Host example.com
Host vps
  Hostname 72.xxx.xxx.xxx

As you can see, you can also use your per-user ssh_config to provide handy aliases for some hosts.