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16. Compatibility with other versions of m4

This chapter describes the many of the differences between this implementation of m4, and of other implementations found under UNIX, such as System V Release 3, Solaris, and BSD flavors. In particular, it lists the known differences and extensions to POSIX. However, the list is not necessarily comprehensive.

At the time of this writing, POSIX 2001 (also known as IEEE Std 1003.1-2001) is the latest standard, although a new version of POSIX is under development and includes several proposals for modifying what m4 is required to do. The requirements for m4 are shared between SUSv3 and POSIX, and can be viewed at http://www.opengroup.org/onlinepubs/000095399/utilities/m4.html.


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16.1 Extensions in GNU M4

This version of m4 contains a few facilities that do not exist in System V m4. These extra facilities are all suppressed by using the `-G' command line option (see section Invoking m4), unless overridden by other command line options.


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16.2 Facilities in System V m4 not in GNU m4

The version of m4 from System V contains a few facilities that have not been implemented in GNU m4 yet. Additionally, POSIX requires some behaviors that GNU m4 has not implemented yet. Relying on these behaviors is non-portable, as a future release of GNU m4 may change.


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16.3 Other incompatibilities

There are a few other incompatibilities between this implementation of m4, and the System V version.


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