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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 Command-Line Options).
• The use of CONVFMT for controlling the conversion of numbers to strings (see Conversion of Strings and Numbers).
• The concept of a numeric string and tighter comparison rules to go with it (see Variable Typing and Comparison Expressions).
• More complete documentation of many of the previously undocumented features of the language.

The following common extensions are not permitted by the POSIX standard:

• \x escape sequences are not recognized (see Escape Sequences).
• Newlines do not act as whitespace to separate fields when FS is equal to a single space (see Examining Fields).
• Newlines are not allowed after ? or : (see Conditional Expressions).
• The synonym func for the keyword function is not recognized (see Function Definition Syntax).
• The operators ** and **= cannot be used in place of ^ and ^= (see Arithmetic Operators, and Assignment Expressions).
• Specifying -Ft on the command line does not set the value of FS to be a single TAB character (see Specifying How Fields Are Separated).
• The fflush built-in function is not supported (see Input/Output Functions).