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(gawk.info)POSIX

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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 (Note:
     Command-Line Options.).

   * The use of `CONVFMT' for controlling the conversion of numbers to
     strings (Note: Conversion of Strings and Numbers.).

   * The concept of a numeric string and tighter comparison rules to go
     with it (Note: 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 (Note: Escape
     Sequences).

   * Newlines do not act as whitespace to separate fields when `FS' is
     equal to a single space (Note: Examining Fields.).

   * Newlines are not allowed after `?' or `:' (Note: Conditional
     Expressions.).

   * The synonym `func' for the keyword `function' is not recognized
     (Note: Function Definition Syntax.).

   * The operators `**' and `**=' cannot be used in place of `^' and
     `^=' (Note: Arithmetic Operators., and Note:
     Assignment Expressions.

   * Specifying `-Ft' on the command line does not set the value of
     `FS' to be a single tab character (Note: Specifying How Fields Are
     Separated.).

   * The `fflush' built-in function is not supported (Note:
     Input/Output Functions.).