Some command languages allow abbreviated forms of the commands. This is really handy. Others allow for CommandLineCompletion? which is also pretty darned handy.
IMHO, this is a critical part of DesigningTextEditors.
The command language will be that implemented by the OS shell. Command languages may also be script languages, with flow-of-control structures, and permit the user to write small programs in the language the shell implements. It may be possible for the editor to execute a shell program rather than an individual underlying OS command, providing greater flexibility in what can be done from the editor.