The confstr function allows an application to determine the
    current setting of certain system parameters, limits, or options
    that are defined by a string value. The function is mainly used
    by applications to find the system default value for the PATH
    environment variable.

    If the following conditions are true, then the confstr function
    copies that value into a len-byte buffer pointed to by buf:

    o  The len argument can be 0 (zero).

    o  The name argument has a system-defined value.

    o  The buf argument is not a NULL pointer.

    If the returned string is longer than len bytes, including the
    terminating null, then the confstr function truncates the string
    to len - 1 bytes and adds a terminating null to the result. The
    application can detect that the string was truncated by comparing
    the value returned by the confstr function with the value of the
    len argument.

    The <limits.h> header file contains system-defined limits. The
    <unistd.h> header file contains system-defined environmental
    variables.

    Also, confstr supports the following three HP-UX symbolic
    constants, which are added to header file <unistd.h>:

    o  _CS_MACHINE_IDENT

    o  _CS_PARTITION_IDENT

    o  _CS_MACHINE_SERIAL