A.5 Extensions in gawk Not in POSIX awk

The GNU implementation, gawk, adds a large number of features. This section lists them in the order they were added to gawk. They can all be disabled with either the --traditional or --posix options (see Options).

Version 2.10 of gawk introduced the following features:

• The AWKPATH environment variable for specifying a path search for the -f command-line option (see Options).
• The IGNORECASE variable and its effects (see Case-sensitivity).
• The /dev/stdin, /dev/stdout, /dev/stderr and /dev/fd/N special file names (see Special Files).

Version 2.13 of gawk introduced the following features:

• The FIELDWIDTHS variable and its effects (see Constant Size).
• The systime and strftime built-in functions for obtaining and printing timestamps (see Time Functions).
• The -W lint option to provide error and portability checking for both the source code and at runtime (see Options).
• The -W compat option to turn off the GNU extensions (see Options).
• The -W posix option for full POSIX compliance (see Options).

Version 2.14 of gawk introduced the following feature:

• The next file statement for skipping to the next data file (see Nextfile Statement).

Version 2.15 of gawk introduced the following features:

• The ARGIND variable, which tracks the movement of FILENAME through ARGV (see Built-in Variables).
• The ERRNO variable, which contains the system error message when getline returns −1 or close fails (see Built-in Variables).
• The /dev/pid, /dev/ppid, /dev/pgrpid, and /dev/user file name interpretation (see Special Files).
• The ability to delete all of an array at once with `delete array' (see Delete).
• The ability to use GNU-style long-named options that start with -- (see Options).
• The --source option for mixing command-line and library-file source code (see Options).

Version 3.0 of gawk introduced the following features:

• IGNORECASE changed, now applying to string comparison as well as regexp operations (see Case-sensitivity).
• The RT variable that contains the input text that matched RS (see Records).
• Full support for both POSIX and GNU regexps (see Regexp).
• The gensub function for more powerful text manipulation (see String Functions).
• The strftime function acquired a default time format, allowing it to be called with no arguments (see Time Functions).
• The ability for FS and for the third argument to split to be null strings (see Single Character Fields).
• The ability for RS to be a regexp (see Records).
• The next file statement became nextfile (see Nextfile Statement).
• The --lint-old option to warn about constructs that are not available in the original Version 7 Unix version of awk (see V7/SVR3.1).
• The -m option and the fflush function from the Bell Laboratories research version of awk (see Options; also see I/O Functions).
• The --re-interval option to provide interval expressions in regexps (see Regexp Operators).
• The --traditional option was added as a better name for --compat (see Options).
• The use of GNU Autoconf to control the configuration process (see Quick Installation).
• Amiga support (see Amiga Installation).

Version 3.1 of gawk introduced the following features:

• The BINMODE special variable for non-POSIX systems, which allows binary I/O for input and/or output files (see PC Using).
• The LINT special variable, which dynamically controls lint warnings (see Built-in Variables).
• The PROCINFO array for providing process-related information (see Built-in Variables).
• The TEXTDOMAIN special variable for setting an application's internationalization text domain (see Built-in Variables, and Internationalization).
• The ability to use octal and hexadecimal constants in awk program source code (see Nondecimal-numbers).
• The `|&' operator for two-way I/O to a coprocess (see Two-way I/O).
• The /inet special files for TCP/IP networking using `|&' (see TCP/IP Networking).
• The optional second argument to close that allows closing one end of a two-way pipe to a coprocess (see Two-way I/O).
• The optional third argument to the match function for capturing text-matching subexpressions within a regexp (see String Functions).
• Positional specifiers in printf formats for making translations easier (see Printf Ordering).
• The asort and asorti functions for sorting arrays (see Array Sorting).
• The bindtextdomain, dcgettext and dcngettext functions for internationalization (see Programmer i18n).
• The extension built-in function and the ability to add new built-in functions dynamically (see Dynamic Extensions).
• The mktime built-in function for creating timestamps (see Time Functions).
• The and, or, xor, compl, lshift, rshift, and strtonum built-in functions (see Bitwise Functions).
• The support for `next file' as two words was removed completely (see Nextfile Statement).
• The --dump-variables option to print a list of all global variables (see Options).
• The --gen-po command-line option and the use of a leading underscore to mark strings that should be translated (see String Extraction).
• The --non-decimal-data option to allow non-decimal input data (see Nondecimal Data).
• The --profile option and pgawk, the profiling version of gawk, for producing execution profiles of awk programs (see Profiling).
• The --enable-portals configuration option to enable special treatment of pathnames that begin with /p as BSD portals (see Portal Files).
• The use of GNU Automake to help in standardizing the configuration process (see Quick Installation).
• The use of GNU gettext for gawk's own message output (see Gawk I18N).
• BeOS support (see BeOS Installation).
• Tandem support (see Tandem Installation).
• The Atari port became officially unsupported (see Atari Installation).
• The source code now uses new-style function definitions, with ansi2knr to convert the code on systems with old compilers.
• The --disable-lint configuration option to disable lint checking at compile time (see Additional Configuration Options).
• POSIX compliance for sub and gsub (see Gory Details).