Exploring Expect

The close Command

When a spawned process closes its connection to Expect, the expect command sees an eof.

Figure 4-1. 

This scenario can also occur in the reverse direction. Expect can close the connection and the spawned process will see an eof.

Figure 4-2. 

By closing the connection, Expect is telling the spawned process that it has nothing more to say to the process. Usually the process takes this as an indication to exit. This is similar to what occurs when you press ^D while manually interacting with a process. The process does not see the ^D. Rather, the system turns this into an eof. The process reads the eof and then responds by closing the connection and exiting.

There is one difference between how Expect and the spawned process treat a closed connection. When Expect closes the connection, the spawned process sees an additional indication in the form of a hangup signal. Most processes take this as an instruction to immediately exit. The net result is very similar to reading an eof. In either case, the process exits. Later in the book, I will go into more detail about what signals are and how you can ignore them or take advantage of them.

From Expect, the command to close the connection to a process is close. It is called as:

close

No matter which side—the Expect process or the spawned ...