code: public boolean isValidPosixFileChar(char c) {
      if ((((c >= 'A') && (c <= 'Z')) || ((c >= 'a') && (c <= 'z')) ||
             ((c >= '0') && (c <= '9'))
             || (c == '.') || (c == '_') || (c == '-'))) {
        return true;
      } else {
        return false;
      }
    }
docs: Test whether the character c belongs to the accepted list of posix
  filename characters A-Za-z0-9._-
  @param c
  @return