title: Allowed characters in Linux environment variable names
body: <p>What characters are allowed in Linux environment variable names? My cursory search of man pages and the web did only produce information about how to work with variables, but not which names are allowed.</p>
  
  <p>I have a Java program that requires an defined environment variable containing a dot, like <code>com.example.fancyproperty</code>. With Windows I can set that variable, but I had no luck setting it in linux (tried in SuSE and Ubuntu). Is that variable name even allowed?</p>