Exploring Expect

Philosophy--Processes Are Smart

The previous chapter demonstrated how to open files or devices and send commands to them with puts. This technique calls upon another program to do the handling of the device. At first glance, you might consider this inefficient. Why run two programs when one will do? Consider that reusing another program allows you to isolate all the device-specific problems in one place. If the tip program already knows about serial devices and how, for example, to choose among baud rates, why burden other programs with the same knowledge?

Ideally, if you just had one program that knew everything about, say, your serial devices, you would not need any others. Or perhaps, other programs could call upon your serial device program when they needed to access a serial device. This is analogous to the concept of device drivers. Unfortunately, real device drivers are not high-level enough to isolate out the device dependencies for our purposes.

It is all too common to have numerous programs (kermit, procomm, tip, cu, etc.) that all do the same thing. The reason for having multiple programs to do the same thing is that one has features that another does not have and vice versa. So you keep them all around. Not only is this a problem when you require both features at the same time, but it is a problem when you upgrade or modify your serial device. For example, if you change some phone numbers in your kermit scripts, you also have to change them in any procomm scripts. Some ...