A.3 Changes Between SVR4 and POSIX awk

The POSIX Command Language and Utilities standard for awk (1992) introduced the following changes into the language:

• The use of -W for implementation-specific options (see section Command-Line Options)
• The use of CONVFMT for controlling the conversion of numbers to strings (see section Conversion of Strings and Numbers)
• The concept of a numeric string and tighter comparison rules to go with it (see section Variable Typing and Comparison Expressions)
• The use of predefined variables as function parameter names is forbidden (see section Function 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 (see section Input/Output Functions)
• The nextfile statement (see section The nextfile Statement)
• The ability to delete all of an array at once with ‘delete array’ (see section The delete Statement)

See section Common Extensions Summary for a list of common extensions not permitted by the POSIX standard.

The 2018 POSIX standard can be found online at https://pubs.opengroup.org/onlinepubs/9699919799/.