It sounds like you are trying to do something complicated. This link may help explain the basics of events TPJ article on events

While playing around, I've noticed some peculiarities with Tk::fileevent. If it's something with alot of output, you may need to throttle it a little bit. For instance, this first example will not produce output, but the second will. I need to study more on this. I believe it boils down to the filehandle needs to "be readable", it won't buffer for you.

#!/usr/bin/perl
use warnings;
use strict;
use Tk;

startpiper();

my $mw = new MainWindow;

my $t = $mw->Scrolled("Text",-width => 80, -height => 25, -wrap => 'no
+ne');
                                             $t->pack(-expand => 1);

$mw->fileevent(\*CHILD, 'readable', [\&fill_text_widget,$t]);
MainLoop;

sub fill_text_widget {
          my($widget) = @_;
          $_ = <CHILD>;
          $widget->insert('end', $_);
          $widget->yview('end');
}

sub startpiper{
open(CHILD, "ls -la |") or die "Can't open: $!";
}
[download]

The following will run

#!/usr/bin/perl
use warnings;
use strict;
use Tk;

open(CHILD, "./fileevent2piper 2>&1 |") or die "Can't open: $!";
                          
my $mw = new MainWindow;
                          
my $t = $mw->Scrolled("Text",-width => 80, -height => 25, -wrap => 'no
+ne');
                                             $t->pack(-expand => 1);
                          
$mw->fileevent(\*CHILD, 'readable', [\&fill_text_widget,$t]);
MainLoop;

sub fill_text_widget {
          my($widget) = @_;
          $_ = <CHILD>;
          $widget->insert('end', $_);
          $widget->yview('end');
}
[download]

And the piper script

#!/usr/bin/perl
$|++;

for my $i ( 0 .. 10) {
        print $i, "\n";
        print `ls -la`;
        sleep 1;
    }
[download]

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