Many times people want to do things like run a program feeding it
information, or doing some setup, then running a command and doing
something with its output, or writing a Tk wrapper for a text only
command.

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Here's an example of wrapping the '''bc''' arbitrary precision arithmetic
language calculator in Tcl.  This might provide one with longer
precision math without implementing one of the extensions discussed
in [Arbitrary Precision Math Procedures].


 #! /usr/tcl84/bin/tclsh
 # Program: bcfe
 # Date: Jan 27, 2003
 # Version: 1.1


 set fe [open "|/bin/bc -l" "r+"]
 fconfigure $fe -buffering none

 puts "Enter expression:"
 set ex 1
 puts -nonewline "bc $ex> "
 flush stdout
 while { [gets stdin input] >= 0 } {
        if { $input == "quit" } {
                break
        }
        puts $fe "$input"
        flush $fe
        incr ex
        gets $fe newans
        puts "Answer is: $newans"
        puts -nonewline "bc $ex> "
        flush stdout
 }



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Derk Gwen succinctly answers the oh-so-frequently-asked question about how to keep Tk "live" while managing
a sub-process in a clt posting 
[http://groups.google.com/groups?q=append+output+rs+rc+readable+group:comp.lang.tcl*&hl=en&lr=&ie=UTF-8&selm=v37uvs8rim6i0f%40corp.supernews.com&rnum=1].

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See [[add in reference to Alex's page]] for lots of ways to communicate
between applications.




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[[ [CL] intends to link in lots of references to related topics:  Tcl and other processes, Tcl and other languages,
the idea of wrapping, ...]]

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[Category Application]