dir 2>&1 doesn't work in Windows. cmd.exe /c dir does.
Following is my updated version. I also had to change -text => $cmdLineText to -textvariable => \$cmdLineText for the Label to see the changes in the variable. 
use warnings;
use strict;
use Tk;
use Tk::Button;
use Tk::Checkbutton;
use Tk::LabEntry;
use Tk::Label;

my $cmdLineText;
my $mw=MainWindow->new(-title=>'Foo Installer');
my $row = 0;

my $w_install = $mw-> Button ( -overrelief=>'raised', -relief=>'raised
+', -text=>'Install', -command=>\&installItems) -> grid(-column=>0, -r
+ow=>++$row, -columnspan=>3, -sticky=>'nsew');

my $w_cmdWindow = $mw->Label (-height=>7, -foreground=>'white', -backg
+round=>'black', -textvariable => \$cmdLineText)->grid(-column=>0, -ro
+w=>++$row, -columnspan=>3, -rowspan=>10, -sticky=>'nsew');

MainLoop;
sub installItems {
  open (FILE, "cmd.exe /c dir|");    #does something
  $cmdLineText = "";
  while (<FILE>) {
    #chomp;
    $cmdLineText .= $_;
  }
  close(FILE);
}

[download]

In reply to Re: How can I redirect Windows command line output into a PerlTk frame by frieduck
in thread How can I redirect Windows command line output into a PerlTk frame by jfrai

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