pack [text .text]

    set result [exec my_command]

    .text insert 1.0 $result


See documentation on [exec] for information about how to pass in command-line arguments and "stdin" data.



[[Is there no comparably reduced example already in the Wiki?]]

If the process is a long running process, this will lock up your GUI.
Checkout the [fileevent] page to see how to run the command with 
open & just get updates as they are available. (Change the line 
'''puts "got: $line"''' to '''.text insert end $line''' and 
possibly add a '''.text see end''')

bbh

----

What about a tk app that talks to a running tcl app in a seperate process - is there an example that shows doing this?
Well, yes, although perhaps it's not obviously labeled that way yet.  "[Inventory of IPC methods]" aims to point to ''all'' the ways to get
two such processes in communication.