title: what does '$::n' mean for perl?
body: <p>Do you know what "$::n;" means ? The section of codes is like below.</p>
  
  <pre><code>use JSON::XS;
  # ...
  open (YI, "| $cmd");
  my $msg = { test =&gt; test };
  my $emsg = encode_json($msg);
  print YI "$msg_inject\n" unless $::n;
  close YI;`
  </code></pre>
  
  <p>I remmeber that I also met $::v before.  What is $::v ? Does it have additional usage ?</p>
  
  <p>I only know $: is reserved word for a perl statment with more lines being filling in a field.</p>
  
  <p>Best regards,</p>
  
  <p>TWLMD.</p>