Display contents in the GUI using tcl - perl

Question

I am new to GUI and i was trying to create a simple GUI in tcl. It have a push button which when pressed runs a code and generates a output '.l' file in the directory. But i want the output to be printed in the GUI itself. SO how am i supposed to change this code to do the task.
proc makeTop { } {
toplevel .top ;#Make the window
#Put things in it
label .top.lab -text "This is output Window" -font "ansi 12 bold"
text .top.txt
.top.txt insert end "XXX.l"
#An option to close the window.
button .top.but -text "Close" -command { destroy .top }
#Pack everything
pack .top.lab .top.txt .top.but
}
label .lab -text "This is perl" -font "ansi 12 bold"
button .but -text "run perl" -command { exec perl run_me }
pack .lab .but
Can anyone help me in displaying the contents of output file XXX.l in the GUI itself???

Answer 1

For simple programs that just prints their results to stdout, then it's simple: exec returns all standard output of the program. So you just need to read the return value of your exec call:
proc exec_and_print {args} {
.top.txt insert end [exec {*}$args]
}
But remember, exec only returns after the program have exited. For long running programs where you want the output to appear immediately in your text box you can use open. If the first character of the file name passed to open is | then open assumes that the string is a command line to be executed. With open you get an i/o channel that you can continuously read from:
proc long_running_exec {args} {
set chan [open "| $args"]
# disable blocking to prevent read from freezing our UI:
fconfigure $chan -blocking 0
# use fileevent to read $chan only when data is available:
fileevent $chan readable {
.top.text insert end [read $chan]
# remember to clean up after ourselves if the program exits:
if {[eoc $chan]} {
close $chan
}
}
}
The long_running_exec function above returns immediately and uses events to read the output. This allows your GUI to continue functioning instead of freezing while the external program runs. To use it simply do:
button .but -text "run perl" -command { long_running_exec perl run_me }
Additional answer:
If the program generates a file as output and you want to simply display the contents of the file then just read the file:
proc exec_and_print {args} {
exec {*}$args
set f [open output_file]
.top.txt insert end [read $f]
close $f
}
If you know where the file is generated but don't know the exact file name then read the manual for glob on how to get a list of directory contents.