Exploring Expect

Disconnecting The Controlling Terminal

It is possible to start a script in the foreground but later have it move itself into the background and disconnect itself from the controlling terminal. This is useful when there is some point in the script after which no further interaction is required.

For example, suppose you want to automate a command that requires you to type in a password but it is inconvenient for you to enter the password when it is needed (e.g., you plan to be asleep later).

You could embed the password in the script or pass the password as an argument to it, but those are pretty risky ideas. A more secure way is to have the script interactively prompt for the password and remember it until it is needed later. The password will not be available in any public place—just in the memory of the Expect process.

In order to read the password in the first place, Expect needs a controlling terminal. After the password is read, Expect will still tie up the terminal—until you log out. To avoid the inconvenience of tying up the controlling terminal (or making you log out and back in again), Expect provides the fork and disconnect commands.