This is an application created by default by the core distribution.
It is a simple shell interpreter, and is frequently used by
developers writing tcl scripts.

A user of tclsh (or of [wish], the interactive tcl shell with Tk automatically
loaded), should be aware that there are a few differences between typing
tcl statements to the shell in interactive mode and typing tcl commands
into a file and then executing it.

   * unknown proc differences - if tclsh is unable to recognize the command typed, the unknown proc is invoked.

   interactive:  unknown will automatically pass command to exec .
   command file:  the coder must specify exec before any non-tcl commands

   * standard output displayed 

   interactive:  stdout appears to the screen when you type commands
   command file:  the coder must specify puts to get the output from a command to display to the screen

   * abbreviations 


I'm unsure what is meant by "abbreviations" above.   Yet another
symptomatic difference of interactive operation is that, when
interactive, the interpreter (by way of [unknown]) takes otherwise-unknown
command names as abbreviations.  Thus in interactive mode it's possible
to write
    set fp [op $myfile]
although a scripted application would require [open] be written out in full.
----
[Category Application], a part of the [Tcl] package.