Exploring Expect

Obtaining Console Output

Historically, the console was a dedicated terminal to which critical messages were sent concerning the status of the computer. The idea was that a person would be watching at all times and could take immediate action if necessary. With modern workstations, there is no physical console with a dedicated operator. Instead, the console is simulated with a dedicated window. For example, in the X window system, the command "xterm -C" starts an xterm window and tells the operating system to send all console messages to it.

Expect can do the same thing with the spawn command. The -console flag redirects all console messages so that they appear to be generated from a spawned process. It is sufficient to spawn any process. Even cat will do.

spawn -console cat

A simple use for this flag is to watch for errors from device drivers. For example, when performing backups, errors writing to the backup media may be sent to the console rather than the backup program. This is a consequence of the way certain drivers are written and is surprisingly common.

By spawning the backup program using the -console flag, it is possible to catch problems with the backup that might not otherwise be reported. In Chapter 17 (p. 380), I will describe how to make an Expect script actively look for a skilled user to fix any problems encountered, and initiate a session for the user connected to the spawned process automatically.

The -console feature can only be used by one program at a time. It is ...