gawk: POSIX
A.3 Changes Between SVR4 and POSIX 'awk'
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The POSIX Command Language and Utilities standard for 'awk' (1992)
introduced the following changes into the language:
Options::)
* The use of 'CONVFMT' for controlling the conversion of numbers to
strings (Conversion)
* The concept of a numeric string and tighter comparison rules to go
with it (Typing and Comparison)
* The use of predefined variables as function parameter names is
forbidden (Definition Syntax)
* More complete documentation of many of the previously undocumented
features of the language
In 2012, a number of extensions that had been commonly available for
many years were finally added to POSIX. They are:
* The 'fflush()' built-in function for flushing buffered output
(I/O Functions)
* The 'nextfile' statement (Nextfile Statement)
* The ability to delete all of an array at once with 'delete ARRAY'
(Delete)
Common Extensions for a list of common extensions not
permitted by the POSIX standard.
The 2008 POSIX standard can be found online at
<http://pubs.opengroup.org/onlinepubs/9699919799/>.