With the DECC$UNIX_LEVEL logical name, you can manage multiple
    C RTL feature logical names at once. By setting a value for
    DECC$UNIX_LEVEL from 1 to 100, you determine the default value
    for groups of feature logical names. The value you set has a
    cumulative effect: the higher the value, the more groups that
    are affected. Setting a value of 20, for example, enables all the
    feature logicals associated with a DECC$UNIX_LEVEL of 20, 10, and
    1.

    The principal logical names affecting UNIX like behavior are
    grouped as follows:

       1    General corrections
       10   Enhancements
       20   UNIX style filenames
       30   UNIX style file attributes
       90   Full UNIX behavior - No concessions to OpenVMS

    Level 30 is appropriate for UNIX like programs such as BASH and
    GNV.

    The DECC$UNIX_LEVEL values and associated groups of affected
    feature logical names are:

    General Corrections          (DECC$UNIX_LEVEL 1)

       DECC$FIXED_LENGTH_SEEK_TO_EOF   1
       DECC$POSIX_SEEK_STREAM_FILE     1
       DECC$SELECT_IGNORES_INVALID_FD  1
       DECC$STRTOL_ERANGE              1
       DECC$VALIDATE_SIGNAL_IN_KILL    1

    General Enhancements        (DECC$UNIX_LEVEL 10)

       DECC$ARGV_PARSE_STYLE           1
       DECC$EFS_CASE_PRESERVE          1
       DECC$STDIO_CTX_EOL              1
       DECC$PIPE_BUFFER_SIZE           4096
       DECC$USE_RAB64                  1

    UNIX style filenames       (DECC$UNIX_LEVEL 20)

       DECC$DISABLE_TO_VMS_LOGNAME_TRANSLATION 1
       DECC$EFS_CHARSET                1
       DECC$FILENAME_UNIX_NO_VERSION   1
       DECC$FILENAME_UNIX_REPORT       1
       DECC$READDIR_DROPDOTNOTYPE      1
       DECC$RENAME_NO_INHERIT          1
       DECC$GLOB_UNIX_STYLE

    UNIX like file attributes     (DECC$UNIX_LEVEL 30)

       DECC$EFS_FILE_TIMESTAMPS        1
       DECC$EXEC_FILEATTR_INHERITANCE  1
       DECC$FILE_OWNER_UNIX            1
       DECC$FILE_PERMISSION_UNIX       1
       DECC$FILE_SHARING               1

    UNIX compliant behavior       (DECC$UNIX_LEVEL 90)

       DECC$FILENAME_UNIX_ONLY         1
       DECC$POSIX_STYLE_UID            1
       DECC$USE_JPI$_CREATOR           1
       DECC$DETACHED_CHILD_PROCESS     1

                                  NOTES

       o  Defining a logical name for an individual feature logical
          supersedes the default value established by DECC$UNIX_
          LEVEL for that feature.

       o  Future revisions of the C RTL may add new feature
          logicals to a given DECC$UNIX_LEVEL. For applications
          that specify that UNIX level, the effect is to enable
          those new feature logicals by default.