HATE: The Use of Tcl

HATE is written entirely in Tcl, John Ousterhout's Tool Command Language. This means that a little familiarity with Tcl is needed in order to devise test scripts or to interface Tcl to your own programs; this is not difficult to acquire. Tcl is easy to read, most of its commands being English-like. There are several reasons for the choice of Tcl.

• Tcl is a "scripting" language analogous to, say, the Unix shells: in particular, it allows external programs to be executed by a Tcl "script" (program) and provides facilities such as regular expressions that make it simple to extract information from the output of external programs.

• Tcl is available for a wide range of platforms, including all flavours of Unix, Microsoft Windows (NT, 95, 3.1), and the Macintosh. Carefully-written Tcl scripts can be used unchanged on all these platforms. The Tcl interpreter is small, robust, and well-written.

• With the expect extensions, Tcl scripts are able to control programs intended for interactive use, including those that perform cursor addressing. For detailed information on expect, look at Don Libes' book Exploring Expect: A Tcl-based Toolkit for Automating Interactive Programs (O'Reilly and Associates, 1994).

• There is a toolkit, known as Tk, that may be used from Tcl scripts for implementing graphical user interfaces (GUIs) -- and such GUIs are portable between platforms. On Unix, Tk GUIs have a Motif appearance; on other systems, they match those of the native windowing system. This makes it possible to integrate HATE-based testing into GUIs written in Tcl, typically by means of a pull-down menu.

• The standard of documentation on both Tcl and Tk is very good: excellent references are John Ousterhout's Tcl and the Tk Toolkit (Addison-Wesley, 1994) and Brent Welch's Practical Programming in Tcl (Prentice-Hall, 1995). Note that Ousterhout's book describes a slightly older version of Tcl/Tk, one that does not have an image-display capability; Welch's book covers a more up-to-date version. Extensive manual pages are available, in both Unix man and HTML formats; you are welcome to peruse the HTML manual pages stored at Essex.

• Tcl, Tk, and a wide range of extensions are available free of charge via the Internet, and Ousterhout has guaranteed that Tcl and Tk will remain freely available. There are also no restrictions on the incorporation of Tcl and Tk into commercial products.