status

    For non-POSIX behavior, a status value of EXIT_SUCCESS (1), EXIT_
    FAILURE (2), or a number from 3 to 255, as follows:

    o  A status value of 0, 1 or EXIT_SUCCESS is translated to the
       OpenVMS SS$_NORMAL status code to return the OpenVMS success
       value.

    o  A status value of 2 or EXIT_FAILURE is translated to an error-
       level exit status. The status value is passed to the parent
       process.

    o  Any other status value is left the same.

    For POSIX behavior:

    o  A status value of 0 is translated to the OpenVMS SS$_NORMAL
       status code to return the OpenVMS success value.

    o  Any other status is returned to the parent process as an
       OpenVMS message symbol with facility set to C, severity
       set to success, and with the status in the message number
       field. For more information on the format of message symbols,
       see "message code" in the VSI OpenVMS Command Definition,
       Librarian, and Message Utilities Manual.

    To get POSIX behavior, include <unistd.h> and compile with the
    _POSIX_EXIT feature-test macro set (either with /DEFINE=_POSIX_
    EXIT, or with #define _POSIX_EXIT at the top of your file, before
    any file inclusions). This behavior is available only on OpenVMS
    Version 7.0 and higher systems.