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//usr/local/ssl/share/doc/perl-Expect-1.21/tutorial/1.A.Intro
Why is this tool useful? Chances are if you are reading this you probably have already used the fine Expect for tcl, and possibly even read Exploring Expect. You are interested in learning how to accomplish the same things you've done in tcl using perl, or perhaps are just totally irritated at tcl. Expect is a generic tool for talking to processes that normally require user interaction. This might be running an ftp client to grab a file, telnetting to a router to grab statistics or reset an interface. Or, as in the case of a place I recently administered, to start up a secure webserver without having to be physically at the machine to enter the super secret password. Expect talks to processes through ptys. To it, a process is mostly just a bidirectional file handle, much the same as a socket. In fact, it is possible to take a filehandle you've already used and pass it off to expect to interact with. Now, something you might say at this point is "well, but there are tools that I can use to do that with for more common protocols like telnet and ftp already, such as Net::Ftp and Net::Telnet. Why would I want to use your tool?". This is true. You might never want to use it. However, there are a few advantages Expect has over similar modules: 1. A consistent interface. You don't have to remember the syntax for the other tools. 2. It is more intuitive (my opinion, of course) because you already know how to use the clients you are familiar with. Once you learn how to talk to a process using Expect you will have an easy time automating your other tasks. 3. It is more versatile. With Expect you can connect multiple processes together, write to log files, talk to sockets, etc. 4. Consistent debugging. Debugging, IMHO, is much easier in Expect than in other tools because you have the ability to watch the interaction take place, and it's really pretty easy to use. One serious disadvantage of Expect is that scripts generated using it are generally non-portable. The way a client 'looks' is important to building a script to talk to it. Interacting with a client on DG-UX may be very different than the equivalent client on SunOS. Or, and ncftp would be a good example of this, a client may be different between versions. Similarly, if an administrator changes versions of a server it might send back different prompts than what you are looking for. These are things you should be aware of.
