A.5 Extensions in gawk Not in POSIX awk

The GNU implementation, gawk, adds a large number of features. They can all be disabled with either the ‘--traditional’ or ‘--posix’ options (see section Command-Line Options).

A number of features have come and gone over the years. This section summarizes the additional features over POSIX awk that are in the current version of gawk.

• Additional built-in variables:
  • - The ARGIND BINMODE, ERRNO, FIELDWIDTHS, FPAT, IGNORECASE, LINT, PROCINFO, RT, and TEXTDOMAIN variables (see section Built-in Variables).
• Special files in I/O redirections:
  • - The ‘/dev/stdin’, ‘/dev/stdout’, ‘/dev/stderr’ and ‘/dev/fd/N’ special file names (see section Special File Names in gawk).
  • - The ‘/inet’, ‘/inet4’, and ‘/inet6’ special files for TCP/IP networking using ‘|&’ to specify which version of the IP protocol to use. (see section Using gawk for Network Programming).
• Changes and/or additions to the language:
  • - The ‘\x’ escape sequence (see section Escape Sequences).
  • - Full support for both POSIX and GNU regexps (see section Regular Expressions).
  • - The ability for FS and for the third argument to split() to be null strings (see section Making Each Character a Separate Field).
  • - The ability for RS to be a regexp (see section How Input Is Split into Records).
  • - The ability to use octal and hexadecimal constants in awk program source code (see section Octal and Hexadecimal Numbers).
  • - The ‘|&’ operator for two-way I/O to a coprocess (see section Two-Way Communications with Another Process).
  • - Indirect function calls (see section Indirect Function Calls).
  • - Directories on the command line produce a warning and are skipped (see section Directories On The Command Line).
• New keywords:
  • - The BEGINFILE and ENDFILE special patterns. (see section The BEGINFILE and ENDFILE Special Patterns).
  • - The ability to delete all of an array at once with ‘delete array’ (see section The delete Statement).
  • - The nextfile statement (see section Using gawk’s nextfile Statement).
  • - The switch statement (see section The switch Statement).
• Changes to standard awk functions:
  • - The optional second argument to close() that allows closing one end of a two-way pipe to a coprocess (see section Two-Way Communications with Another Process).
  • - POSIX compliance for gsub() and sub().
  • - The length() function accepts an array argument and returns the number of elements in the array (see section String-Manipulation Functions).
  • - The optional third argument to the match() function for capturing text-matching subexpressions within a regexp (see section String-Manipulation Functions).
  • - Positional specifiers in printf formats for making translations easier (see section Rearranging printf Arguments).
  • - The split() function’s additional optional fourth argument which is an array to hold the text of the field separators. (see section String-Manipulation Functions).
• Additional functions only in gawk:
  • - The and(), compl(), lshift(), or(), rshift(), and xor() functions for bit manipulation (see section Bit-Manipulation Functions).
  • - The asort() and asorti() functions for sorting arrays (see section Controlling Array Traversal and Array Sorting).
  • - The bindtextdomain(), dcgettext() and dcngettext() functions for internationalization (see section Internationalizing awk Programs).
  • - The extension() built-in function and the ability to add new functions dynamically (see section Adding New Built-in Functions to gawk).
  • - The fflush() function from Brian Kernighan’s version of awk (see section Input/Output Functions).
  • - The gensub(), patsplit(), and strtonum() functions for more powerful text manipulation (see section String-Manipulation Functions).
  • - The mktime(), systime(), and strftime() functions for working with timestamps (see section Time Functions).
• Changes and/or additions in the command-line options:
  • - The AWKPATH environment variable for specifying a path search for the ‘-f’ command-line option (see section Command-Line Options).
  • - The ability to use GNU-style long-named options that start with ‘--’ and the ‘--characters-as-bytes’, ‘--compat’, ‘--dump-variables’, ‘--exec’, ‘--gen-pot’, ‘--lint’, ‘--lint-old’, ‘--non-decimal-data’, ‘--posix’, ‘--profile’, ‘--re-interval’, ‘--sandbox’, ‘--source’, ‘--traditional’, and ‘--use-lc-numeric’ options (see section Command-Line Options).
• Support for the following obsolete systems was removed from the code and the documentation for gawk version 4.0:
  • - Amiga
  • - Atari
  • - BeOS
  • - Cray
  • - MIPS RiscOS
  • - MS-DOS with the Microsoft Compiler
  • - MS-Windows with the Microsoft Compiler
  • - NeXT
  • - SunOS 3.x, Sun 386 (Road Runner)
  • - Tandem (non-POSIX)
  • - Prestandard VAX C compiler for VAX/VMS