Exploring Expect

Expect Versions

Like any software, new releases of Expect appear from time to time as features are added and bugs are found and fixed. The exp_version command is useful for dealing with version mismatches. It can verify that the script is appropriate for the current Expect executable and prevent the script from continuing if not. With no arguments, Expect reports the current version.

expect1.1> exp_version
5.9.0

This version may then be placed in your script in an exp_version command. If you know that you are not using features of recent versions, you can specify an earlier version.

The version checking is relatively simple and will not catch all incompatibilities, but it will catch many flagrant problems. The checking depends on the way Expect versions are assigned. Expect versions consist of three numbers separated by dots. First is the major number. Unless they are very simple, scripts written for versions of Expect with a different major number will almost certainly not work. In this case, exp_version generates an error and returns an appropriate message.

For example, if you are using Expect 5.3.0, you can insert the following command in your script:

if [catch {exp_version 5.3.0} msg] {
    puts "warning: $msg"
}

If your script is run on a much older version of Expect (e.g., 4.3.0), the script will print a warning that the script was expecting a different version of Expect.

The second number is the minor number. Scripts written for a version with a greater minor number than the current ...