Exploring Expect

Is There More To Tcl?

This chapter has covered most of the Tcl commands and data structures. I will expand on a few of these descriptions later in the book, but for the most part, you have now seen the entire Tcl language.

Even though Tcl is a small language, it is capable of handling very large and sophisticated scripts. However, Tcl was originally designed for writing small scripts with most of the work being done in the underlying commands themselves. Indeed, Tcl supports the ability to add additional commands written in other languages such as C and C++. This is useful for commands that must be very fast or do something unusual (such as the Expect commands do).

Fortunately, the need to resort to implementing your own commands is growing increasingly rare. People have already written commands for just about anything you can imagine. They are packaged into collections called extensions and are available from the Tcl archive. I have already mentioned [incr Tcl] which provides commands for object-oriented programming. Another popular extension is TclX, which provides commands for most of the UNIX system and library calls. There are a variety of extensions to support different databases (e.g., SQL, Oracle, Dbm). And there are many extensions to support graphics (e.g., SIPP, GL, PHIGS). These extensions and others are described in the Tcl FAQ (page 20). In Chapter 22 (p. 507), I will describe how to add existing extensions to Expect.

If none of these extensions provides what you are ...