title: interpolation of hashed format string
body: <p>I am working on a perl cgi-script.
  It should handle some kind of database where print layouts and the values to print are stored in a hash. Here comes my code snippet:</p>
  
  <pre><code>    my $va=1;
      my $vb=2;
      my $fa="";
      my $fb="";
      my %h=( 'format' =&gt; { 'a' =&gt; "This is the value of variable \$va: $va",
                            'b' =&gt; "This is the value of variable \$vb: $vb"
                          },
              'values' =&gt; { 'a' =&gt; "value A",
                            'b' =&gt; "value B"
                          }
            );
      $fa=$h{'format'}-&gt;{'a'};
      $fb=$h{'format'}-&gt;{'b'};
      $va=$h{'values'}-&gt;{'a'};
      $vb=$h{'values'}-&gt;{'b'};
      print "$fa&lt;br/&gt;\n";
      print "$fb&lt;br/&gt;\n";
      $va=3;
      $vb=4;
      print "$fa&lt;br/&gt;\n";
      print "$fb&lt;br/&gt;\n";
  </code></pre>
  
  <p>Until now I got only this (wrong) printout:</p>
  
  <pre><code>   This is the value of variable $va: 1
     This is the value of variable $vb: 2
     This is the value of variable $va: 1
     This is the value of variable $vb: 2
  </code></pre>
  
  <p>What I do expect is:</p>
  
  <pre><code>   This is the value of variable $va: value A
     This is the value of variable $vb: value B
     This is the value of variable $va: 3
     This is the value of variable $vb: 4
  </code></pre>
  
  <p>What could be the reason that the interpolation of the format-strings stored in the hash does not work?</p>