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 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 predefined variables:
  • The ARGIND, BINMODE, ERRNO, FIELDWIDTHS, FPAT, IGNORECASE, LINT, PROCINFO, RT, and TEXTDOMAIN variables (see Predefined Variables)
• Special files in I/O redirections:
  • The /dev/stdin, /dev/stdout, /dev/stderr, and /dev/fd/N special file names (see 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 Using gawk for Network Programming)
• Changes and/or additions to the language:
  • The ‘\x’ escape sequence (see Escape Sequences)
  • Full support for both POSIX and GNU regexps (see Regular Expressions)
  • The ability for FS and for the third argument to split() to be null strings (see Making Each Character a Separate Field)
  • The ability for RS to be a regexp (see How Input Is Split into Records)
  • The ability to use octal and hexadecimal constants in awk program source code (see Octal and Hexadecimal Numbers)
  • The ‘|&’ operator for two-way I/O to a coprocess (see Two-Way Communications with Another Process)
  • Indirect function calls (see Indirect Function Calls)
  • Directories on the command line produce a warning and are skipped (see Directories on the Command Line)
  • Output with print and printf need not be fatal (see Enabling Nonfatal Output)
  • Namespaces and the use of :: to designate an identifier within a namespace (see Namespaces in gawk).
• New keywords:
  • The BEGINFILE and ENDFILE special patterns (see The BEGINFILE and ENDFILE Special Patterns)
  • The switch statement (see 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 Two-Way Communications with Another Process)
  • POSIX compliance for gsub() and sub() with --posix
  • The length() function accepts an array argument and returns the number of elements in the array (see String-Manipulation Functions)
  • The optional third argument to the match() function for capturing text-matching subexpressions within a regexp (see String-Manipulation Functions)
  • Positional specifiers in printf formats for making translations easier (see Rearranging printf Arguments)
  • The split() function’s additional optional fourth argument, which is an array to hold the text of the field separators (see String-Manipulation Functions)
• Additional functions only in gawk:
  • The gensub(), patsplit(), and strtonum() functions for more powerful text manipulation (see String-Manipulation Functions)
  • The asort() and asorti() functions for sorting arrays (see Controlling Array Traversal and Array Sorting)
  • The mktime(), systime(), and strftime() functions for working with timestamps (see Time Functions)
  • The and(), compl(), lshift(), or(), rshift(), and xor() functions for bit manipulation (see Bit-Manipulation Functions)
  • The isarray() function to check whether a variable is an array, and the more general typeof() function (see Getting Type Information)
  • The mkbool() function to create a Boolean value (see Generating Boolean Values)
  • The bindtextdomain(), dcgettext(), and dcngettext() functions for internationalization (see Internationalizing awk Programs)
• 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 Command-Line Options)
  • The AWKLIBPATH environment variable for specifying a path search for the -l command-line option (see Command-Line Options)
  • The -b, -c, -C, -d, -D, -e, -E, -g, -h, -i, -l, -L, -M, -n, -N, -o, -O, -p, -P, -r, -s, -S, -t, and -V short options. Also, the ability to use GNU-style long-named options that start with --, and the --assign, --bignum, --characters-as-bytes, --copyright, --debug, --dump-variables, --exec, --field-separator, --file, --gen-pot, --help, --include, --lint, --lint-old, --load, --non-decimal-data, --optimize, --no-optimize, --posix, --pretty-print, --profile, --re-interval, --sandbox, --source, --traditional, --use-lc-numeric, and --version long options (see 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
  • GCC for Alpha has not been tested for a while.
• Support for the following obsolete system was removed from the code for gawk version 4.1:
  • Ultrix
• Support for the following systems was removed from the code for gawk version 4.2:
  • MirBSD
  • GNU/Linux on Alpha
• Support for the following systems was removed from the code for gawk version 5.2:
  • OS/2
  • DJGPP
  • VAX/VMS

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