title: What is the reason for the warning "Unquoted string … may clash with future reserved word"?
body: <p>I am trying to work through all the warnings in a Perl program, and having some trouble with this one.</p>
  <pre><code>Unquoted string &quot;lib&quot; may clash with future reserved word at /home/user/bin/ttt.v01.pl line 17.
      line 17: use lib ( &quot;${HOME}/.lib&quot; );
  Unquoted string &quot;sync&quot; may clash with future reserved word at /home/user/bin/ttt.v01.pl line 23.
      line 23: our $SYNC_HOSTS = &quot;${HOME}/.sync.hosts&quot;;
  Unquoted string &quot;config&quot; may clash with future reserved word at /home/user/bin/ttt.v01.pl line 28.
      line 28: our $USAGE_TEXT = &quot;[-hd] -a &lt;config&gt; -l &lt;location&gt;&quot;;
  </code></pre>
  <p>From <a href="http://p3rl.org/diag" rel="nofollow noreferrer">perldiag</a>:</p>
  <blockquote>
  <p>Unquoted string &quot;%s&quot; may clash with future reserved word</p>
  <p>(W reserved) You used a bareword that might someday be claimed as a reserved word. It's best to put such a word in quotes, or capitalize it somehow, or insert an underbar into it. You might also declare it as a subroutine.</p>
  </blockquote>
  <p>I have these all double quoted, and so I'm not sure what I'm missing.</p>