The name Tcl is derived from Tool Command Language and is pronounced tickle. Tcl is a radically simple open-source interpreted programming language that provides common facilities such as variables, procedures, and control structures as well as many useful features that are not found in any other major language.n most Linux systems, Tcl/Tk is already installed. You can find out by typing tclsh at a console prompt (xterm or such). If a % prompt appears, you're already set. Just to make sure, type info pa at the % prompt to see the patchlevel (e.g. 8.4.9) and info na to see where the executable is located in the file system.