The POSIX Command Language and Utilities standard for
introduced the following changes into the language:
CONVFMTfor controlling the conversion of numbers to strings (see Conversion)
In 2012, a number of extensions that had been commonly available for many years were finally added to POSIX. They are:
fflush()built-in function for flushing buffered output (see I/O Functions)
nextfilestatement (see Nextfile Statement)
See Common Extensions, for a list of common extensions not permitted by the POSIX standard.
The 2008 POSIX standard can be found online at http://www.opengroup.org/onlinepubs/9699919799/.