Expect is a program that “talks” to other interactive programs according to a script.  Following the script, Expect knows what can be expected from a program and what the correct response should be.  An interpreted language provides branching and high-level control structures to direct the dialogue.  In addition, the user can take control and interact directly when desired, afterward returning control to the script.  Expect is based on TCL.

Expectk is a mixture of Expect and Tk.  It behaves just like Expect and Tk’s wish.  Expect can also be used directly in C or C++ (that is, without Tcl).  See libexpect(3).

The name “Expect” comes from the idea of send/expect sequences popularized by uucp, kermit and other modem control programs.  However unlike uucp, Expect is generalized so that it can be run as a user-level command with any program and task in mind.  Expect can actually talk to several programs at the same time.

In general, Expect is useful for running any program which requires interaction between the program and the user.  All that is necessary is that the interaction can be characterized programmatically.  Expect can also give the user back control (without halting the program being controlled) if desired.  Similarly, the user can return control to the script at any time.