title: What characters should be restricted from a Unix file name?
body: <p>Consider a <strong>Save As</strong> dialog with a free text entry where the user enters a file name as free text, then clicks a <strong>Save</strong> button.  The software then validates the file name, and saves the file if the name is valid.</p>
  
  <p>On a Unix file system, what rules should be applied in the validation such that:</p>
  
  <ul>
  <li>The name will not be difficult to manipulate later in terms of escaping special characters, etc.</li>
  <li>The rules are not so restrictive that saving a file becomes non-user-friendly.</li>
  </ul>
  
  <p>So basically, what is the <em>minimum</em> set of characters that should be restricted from a Unix file name?</p>