If you have a string that you know works, put code like

if ($string_from_gui ne 'this is the string that works') {
  die "$string is not the same string!\n";
}
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the following code works warning untested

use Net::SSH::Perl;

my $ssh = Net::SSH::Perl->new("myhost", debug => 1, protocol => 2);
$ssh->login("myUser", "myPassword");
my ($out, $error) = $ssh->cmd("pwd");
print $out . "\n";
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This code produces the error, "input must be 8 bytes long at /usr/lib/perl5/site_perl/5.8/cygwin/Crypt/DES.pm line 57"

use Tk;
use Net::SSH::Perl;

my $username;
my $password;

my $mw = MainWindow->new();
my $entry1 = $mw->Entry(-textvariable => \$username)->pack();
my $entry2 = $mw->Entry(-textvariable => \$password)->pack();
my $button = $mw->Button(
  -command => 
    sub 
    {
      my $ssh = Net::SSH::Perl->new("myhost", debug => 1, protocol => 
+2);
      $ssh->login($username, $password);
      my ($out, $error) = $ssh->cmd("pwd");
      print $out . "\n";
    }
)->pack();

MainLoop;
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