m4: Platform macros
13.1 Determining the platform
=============================
Sometimes it is desirable for an input file to know which platform 'm4'
is running on. GNU 'm4' provides several macros that are predefined to
expand to the empty string; checking for their existence will confirm
platform details.
-- Optional builtin: __gnu__
-- Optional builtin: __os2__
-- Optional builtin: os2
-- Optional builtin: __unix__
-- Optional builtin: unix
-- Optional builtin: __windows__
-- Optional builtin: windows
Each of these macros is conditionally defined as needed to describe
the environment of 'm4'. If defined, each macro expands to the
empty string. For now, these macros silently ignore all arguments,
but in a future release of M4, they might warn if arguments are
present.
When GNU extensions are in effect (that is, when you did not use the
'-G' option, ⇒Invoking m4 Limits control.), GNU 'm4' will define
the macro '__gnu__' to expand to the empty string.
$ m4
__gnu__
=>
__gnu__(`ignored')
=>
Extensions are ifdef(`__gnu__', `active', `inactive')
=>Extensions are active
$ m4 -G
__gnu__
=>__gnu__
__gnu__(`ignored')
=>__gnu__(ignored)
Extensions are ifdef(`__gnu__', `active', `inactive')
=>Extensions are inactive
On UNIX systems, GNU 'm4' will define '__unix__' by default, or
'unix' when the '-G' option is specified.
On native Windows systems, GNU 'm4' will define '__windows__' by
default, or 'windows' when the '-G' option is specified.
On OS/2 systems, GNU 'm4' will define '__os2__' by default, or 'os2'
when the '-G' option is specified.
If GNU 'm4' does not provide a platform macro for your system, please
report that as a bug.
define(`provided', `0')
=>
ifdef(`__unix__', `define(`provided', incr(provided))')
=>
ifdef(`__windows__', `define(`provided', incr(provided))')
=>
ifdef(`__os2__', `define(`provided', incr(provided))')
=>
provided
=>1
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