Many modern human-computer interfaces are difficult for people to use. This is often because these interfaces make no significant attempt to communicate with the people who use them. In other words, these interfaces are uncooperative: They do not adapt themselves to their users' needs and they are insensitive to human foibles. Ordinary command line interfaces such as that of the UNIX C shell (csh) are intolerant of even the most simple input errors, even when those errors have obvious corrections. An "intelligent" UNIX shell interface, on the other hand, would make use of knowledge and interaction context in order to interpret --- and as necessary, correct --- its users' commands. Valet is a prototype of such an "intelligent" interface to the UNIX C shell. Valet adds knowledge-based parsing and input correction to the shell by encapsulating an ordinary C shell process within a framework that allows Valet to control the shell's input and output. Valet intercepts shell commands and par...