String safeEnvVarName(String name) {
    StringBuilder safe = new StringBuilder();
    int len = name.length();

    for (int i = 0; i < len; i++) {
      char c = name.charAt(i);
      char s;
      if ((c >= '0' && c <= '9') || (c >= 'A' && c <= 'Z')
          || (c >= 'a' && c <= 'z')) {
        s = c;
      } else {
        s = '_';
      }
      safe.append(s);
    }
    return safe.toString();
  }
sends periodic reports back to the tracker.
ql/src/java/org/apache/hadoop/hive/ql/exec/ScriptOperator.java