《Bonus Chapter A》.pdfVIP

Bonus Chapter A Tcl: Tool Command Language In this chapter, we’ll take a look at an exciting development in the Linux world: an extensible, embeddable programming language that is taking the community by storm. Tcl (pronounced tickle) has been developed by John Ousterhout and others over a number of years and is now maintained by Scriptics (). It has become a popular choice of programming language for a diverse range of applications, ranging from fast prototype tools through extension languages to industrial control applications. Tcl is also available on other platforms, including Microsoft Windows and Apple MacOS. We’ll take a look at some of the key features of Tcl, including its extensibility and its use as the interactive interface to new applications, and you’ll also see some of the extensions and applications that have been created. Some of the things we’ll be covering in this chapter are ❑ Tcl commands and control structures ❑ Quoting and substitution ❑ Strings and lists in Tcl ❑ Input and output ❑ Tcl extensions and applications A Tcl Overview We begin our look at Tcl with the basics: how to write and execute Tcl programs and the features of the language. Our First Tcl Program To see how Tcl programs are created and executed, let’s write a very simple “Hello World“ program, hello.tcl. Here’s the source of such a program: set s Hello World puts $s Tcl is an interpreted language, and Tcl programs are often referred to as scripts. In this respect, Tcl and the UNIX shell have a lot in common. In fact, Tcl scripts need to be executed by a Tcl shell, called tclsh. Let’s run our sample script using tclsh. Note that running a Tcl program this way requires only file read permission. $ tclsh he