UNIX has an almost uncountable variety of scripting languages available. These vary from the shell which you run in your "xterm" window to the magnificence which is Perl . Most of these scripting languages have something in common, and the more popular ones are based around C type language constructs.
A script file is a list of commands which a shell interpreter reads and executes. The first line in a script file generally has a line which indicates what interpreter to run. The rest of the file is just a sequence of commands, most often just like those you can run on your command line. Script languages include some method for manipulating variables and data.
Seeing as this is a tcl/tk tutorial, we'll use the tcl/tk shells as our example. The tcl/tk package is actually two products: tcl and tk; where tcl is the actual scripting language and tk is an extension for using X widgets (see the tk section). The tcl interpreter is called "tclsh". If your system supports the "which" command you can run: