#define _POSIX_C_SOURCE
     #define _APPLE_C_SOURE
     #define _NONSTD_SOURCE
     #define __LP64__

DESCRIPTION

     Setting the environment variable COMMAND_MODE to the value legacy causes
     utility programs to behave as closely to Mac OS X 10.3's utility programs
     as possible.  When in this mode all of 10.3's flags are accepted, and in
     some cases extra flags are accepted, but no flags that were used in 10.3
     will have been removed or changed in meaning.  Any behavioral changes in
     this mode are documented in the LEGACY sections of the individual utili-
     ties.

     Setting the environment variable COMMAND_MODE to the value unix03 causes
     utility programs to obey the Version 3 of the Single UNIX Specification
     (``SUSv3'') standards even if doing so would alter the behavior of flags
     used in 10.3.

     COMMAND_MODE's value is case insensitive and if it is unset or set to
     something other than legacy or unix03 it behaves as if it were set to
     unix03.

     Defining _NONSTD_SOURCE causes library and kernel calls to behave as
     closely to Mac OS X 10.3's library and kernel calls as possible.  Any
     behavioral changes in this mode are documented in the LEGACY sections of
     the individual function calls.

     Defining any of _POSIX_C_SOURCE, _APPLE_C_SOURE, or __LP64__ causes
     library and kernel calls to conform to Version 3 of the Single UNIX
     Specification (``SUSv3'') standards even if doing so would alter the
     behavior of functions used in 10.3.  Defining _POSIX_C_SOURCE also
     removes functions, types, and other interfaces that are not part of
     Version 3 of the Single UNIX Specification (``SUSv3'') from the normal C
     namespace, while _APPLE_C_SOURE does not.

     Failing to define any of those symbols currently acts as if you have
     defined _NONSTD_SOURCE but it is expected that in a future OS X release
     the default behavior will change to be as if _APPLE_C_SOURE were defined.

STANDARDS

     With COMMAND_MODE set to unix2003 utility functions conform to Version 3
     of the Single UNIX Specification (``SUSv3'')

     With _POSIX_C_SOURCE, _APPLE_C_SOURE, or __LP64__ system and library
     calls conform to Version 3 of the Single UNIX Specification (``SUSv3'')

BUGS

     Different parts of a program can be compiled with different compatibility
     settings.  The resultant program will normally work as expected, for
     example a regex created by the Version 3 of the Single UNIX Specification