Was test3 suppose to actually run in the terminal?

I do not think what you wrote will work this way (it didn't for me).

However, if we change test3.pl to produce something simple with a delay (sleep) like this: 
#!/usr/bin/perl -w
# the new test3.pl
use strict;

$|=1; #NECESSARY

print "Write something: \n";

my $it=1;
until ($it == 5) {
        print "line $it...\n";
        sleep 1; $it++
}

[download]
Then your problem becomes comprehensible: run alone, this test3 produces five lines of text 1 second apart, but run from test.pl (the Tk) you wait five seconds and then see the five lines.

In addition to adding "$|=1;" to test3.pl, you need to add this Tk command to test.pl, in the loop after the text insert: 

        $text_box -> insert ("end", $_);
        $main->update;

[download]
Now you can watch the five lines appear one at a time, the same way they would if they were logging a time-consuming process.

In reply to Re: Processing STDOUT of a called perl script during execution by halfcountplus
in thread Processing STDOUT of a called perl script during execution by jcorso

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