code: static String resolveVariables(String string) {
        if (string == null) {
           return null;
        }
  
        String rval = string;
        Matcher m = STRING_SUBSTITUTION.matcher(string);
        while (m.find()) {
           if (getInstance().properties.containsKey(m.group(1))) {
              rval = rval.replaceAll(Pattern.quote(m.group(0)), get(m.group(1)).asString());
           } else if (System.getProperties().contains(m.group(1))) {
              rval = rval.replaceAll(Pattern.quote(m.group(0)), System.getProperties().get(m.group(1)).toString());
           } else if (System.getenv().containsKey(m.group(1))) {
              rval = rval.replaceAll(Pattern.quote(m.group(0)), System.getenv().get(m.group(1)));
           }
        }
        return rval;
     }
docs: Resolve variables string.
  
  @param string the string
  @return the string