Purpose: to provide guidelines, tips, techniques, etc. on writing
Tcl/Tk/etc. scripts that ''wrap'' around an existing command
line oriented application.

By ''wrap'', I mean that the resulting script provides some
additional ease of use or functionality over the original
program, and that the user typically has minimal knowledge that
the original application even exists.

A common example is the creation of a [GUI] interface for a command line application.


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Many people take advantage of [Expect] and [Tk] in writing
GUI applications which interact with a character oriented 
application.

Expect is quite useful when you are wanting to interact
with an application that is written to interact with users directly
via the terminal.
One neat example that the Expect book discussions is wrapping a command like ftp, for instance, and then providing your own ''hooks'' for adding new commands - say to gzip or ungzip files on your machine, or to define ''macros'' to perform common sets of ftp actions, etc.

[Tcl] and [Tk] work just fine for writing application that take
additional arguments or use the GUI to gather values to then be supplied
to the wrapped command via its command line.





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[[Lots more pointers:  [Fortran] pages, [wrap] references, 
RE series, CUJ article, ...]]