Exploring Expect

Chapter 12. Send

In this chapter, I will provide more detail about the send command, including its ability to send strings with special timings between the letters of a string. I will revisit the concepts from the previous two chapters—dealing with multiple processes—in the context of send. Finally, I will describe some interactions between send and other parts of Expect such as how to send without echoing.

The descriptions in this chapter will explicitly refer to the send command, but most of them apply to the related commands send_user, send_error, and send_tty.

Implicit Versus Explicit Spawn Ids

The previous chapter showed the differences between controlling expect with spawn_id versus using the -i flag. The send command can be controlled in the same way. For example, the two lines are equivalent—both send the string foo to the process corresponding to the spawn id in the proc variable.

set spawn_id $proc; send "foo"
send −i $proc "foo"

While the first line is longer, setting the spawn id is simpler if a single process is the focus of interaction for a group of commands. For example, if a login is performed, the implicit method (using spawn_id) looks like this:

set spawn_id $proc
expect "login:"
send "$name\r"
expect "Password:"
send "$password\r"
expect "$prompt"

Using explicit −i parameters requires more characters and is more difficult to read.

expect −i $proc "login:"
send −i $proc "$name\r"
expect −i $proc "Password:"
send −i $proc "$password\r"
expect −i $proc "$prompt"

Setting ...