#!/usr/bin/perl

use strict;
use warnings;

#my $number = get_number('one');
#print "$number\n";

for (qw(one two three)){
  my $number = get_number($_);
  print "$number\n";
}

{
  my $hash_ref;
  sub get_number{
    my ($num) = @_;
    unless (defined $hash_ref){
      while (<DATA>){
        chomp;
        my ($str, $num) = split /\|/;
        $hash_ref->{$str} = $num;
      }
    }
    return $hash_ref->{$num};
  }
}

__DATA__
one|1
two|2
three|3

##</code><code>##

Modification of a read-only value attempted at closure_test.pl line 19.

##</code><code>##

1
1
2
3