Perl/Tk saves your favourite tools

• qx(myprogram) to wait for the result, and then reformat that into a Tk-interface, or
• open("myprogram |") to process each line of output of the program the moment it is produced. In this case, the program and your Perl/Tk program run in parallel.

Two-way communication is simple to start but...

• both programs must flush each line: only few Unix commands can do that.
• Open3 requires select() instead of just <>

In general, communication is only possible if both programs are aware of it. In most case, you need both programs to turn internal buffering off, certainly in case of two-way communication.