Here is a way. I have the validation set up to be between 0 and 100, as integer, but you can change the regex to include a . for real values.

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

my $top = MainWindow->new();
my %entries;

for(1..4){
 $entries{$_}{'value'} ||= 0;
 $entries{$_}{'entry'} = $top->Entry(
     -textvariable => \$entries{$_}{'value'},
     -width        => 5,
     -validate     => 'key',
     -vcmd         => \&validate,
  )->pack;
}

MainLoop;

#have to make sure empty value has numeric context 
sub validate{
  my $val = shift;
  $val ||= 0;
  #get alphas and punctuation out 
  if( $val !~ /^\d+$/ ){ return 0 }
  if (($val >= 0) and ($val <= 100)) {return 1}
    else{ return 0 }
}
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