The realpath function returns an absolute pathname from the
    POSIX root. The generated pathname is stored as a null-terminated
    string, up to a maximum of PATH_MAX bytes, in the buffer pointed
    to by resolved_name.

    The realpath function is supported only in POSIX-compliant modes
    (that is, with DECC$POSIX_COMPLIANT_PATHNAMES defined to one of
    the allowed values).

    See also symlink, unlink, readlink, lchown, and lstat.