The $_ of your for loop is aliased to the read-only strings qw(one two three). The while loop inside the sub overwrites $_, hence the "Modification of a read-only value attempted" error. If you add the line: 

    local $_;

[download]
inside your sub get_number it works. Generally, mangling $_ inside a subroutine is poor form.

Update: a cleaner way to ensure the sub plays well with others is to simply change the while loop to use a lexical rather than the implicit $_: 

      while (defined(my $d = <DATA>)){
        chomp $d;
        my ($str, $num) = split /\|/, $d;
        $hash_ref->{$str} = $num;
      }

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In reply to Re: Closure producing 'Modification of read-only value' error by eyepopslikeamosquito
in thread Closure producing 'Modification of read-only value' error by wfsp

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