The docs for validation are not very clear in Tk::Entry, but the -validatecommand callback is designed to accept a return of 1, 0, or -1 from the callback.

You may squeeze some other functionality out of it, but I wouldn't count on it working the way you expect. Here is how I might do it.

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

my $mw = MainWindow->new;

my %ents;

for( my $i=0;$i<=5;$i++)
  {

   $ents{$i}  = $mw->Entry( -bg => 'white',
                        )->pack();

   $ents{$i}->bind('<Return>', \&display  );

  }



MainLoop;


sub display {

  foreach my $ent (sort keys %ents ){
    print  $ents{$ent}->get(),"\n";
   }

print "\n\n";

}
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