Exploring Expect

The return Action

By default, the return command does not behave in a way analogous to break or continue. The return command does not cause the caller to return. Instead, when used as an action, return causes interact itself to return.

For example, consider the following commands:

interact "X" return
puts "interact done"

If the user presses X, the interact command returns and the puts command executes.

This behavior is very useful when you have a problem that is almost automated but has sections that require attention. The script will do most of the work, but you can grab control when necessary. You can interact and then return control to the script.

For example, fsck, the file system checker, looks for discrepancies in the file system. fsck describes the problems it encounters and interactively asks whether it should fix the problem. fsck waits for a y or n as an answer. The following script automatically answers one type of question yes and another type no. Everything else causes control to be turned over to the user via the interact command.

for {} 1 {} {
    expect {
        eof                    break
        "UNREF FILE*CLEAR\\?"  {send "y\r"}
        "BAD INODE*FIX\\?"     {send "n\r"}
        "\\? "                 {interact + return}
    }
}

When the user is through interacting, a plus causes interact to return, after which the script resumes control and continues answering questions.

In this example, control is completely turned over to the user. This is especially useful when the situation is very complicated and the user might need to explore things ...