[WJG] (25/12/23) I'm familiar with the use of Tcl/Tk to act as a GUI front end for console applications: set a command and parameters string, exec/open the application and then gather its output. But, I'm having ongoing issues with both '''talking''' and '''listening''' to a console application. 

The example I have below is uding ''hoichess'', a simple Linux chess engine available from most repositories. When the script in run in a console, ''hoichess'' executes and any ouput that it writes to stdout is caught and displayed in the text widget.

If a valid chess move (lets say e4) is entered from the console ''hoichess'' reads it and a couple of seconds or later its move is displayed in the textbox. However, if a move is typed in the entry widget and returned, the contents are put to the console but these are ignored by ''hoichess''. What am I missing out on? I've tried every which way that I can think of but to no avail. 

Anyone got any ideas?
 
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# !/bin/sh
# the next line restarts using tclsh \
exec tclsh "$0" "$@"

package require Tk
text .t -yscrollcommand {.s set} -state disabled
entry .e -textvar e

scrollbar .s -orient vertical -command {.t yview}
pack .s -side right -fill y
pack .t -side left -fill both -expand 1
pack .e  

proc receive {chan} {
    .t configure -state normal
    .t insert end [read $chan]
    .t configure -state disabled
    .t see end
    if {[eof $chan]} { close $chan }
}


# Run hoichess and capture output
set command {hoichess -x off } 

set chan [open |[concat $command 2>@1]] ;# 0 = stdin 1 = stdout 2 = stderr
fconfigure $chan -blocking 0
fileevent $chan readable [list receive $chan]

# ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# running from terminal is fine, imput read, output loaded by script
# ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# neither one of these output types appear to be read by hoichess, why?
bind .e <Return> { 
        puts stderr $e ; flush stderr
        puts stdout $e ; flush stdout 
        }


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