Extensions in gawk Not in POSIX awk

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

Version 2.10 of gawk introduced these features:

• The AWKPATH environment variable for specifying a path search for the `-f' command line option (see section Command Line Options).
• The IGNORECASE variable and its effects (see section Case-sensitivity in Matching).
• The `/dev/stdin', `/dev/stdout', `/dev/stderr', and `/dev/fd/n' file name interpretation (see section Special File Names in gawk).

Version 2.13 of gawk introduced these features:

• The FIELDWIDTHS variable and its effects (see section Reading Fixed-width Data).
• The systime and strftime built-in functions for obtaining and printing time stamps (see section Functions for Dealing with Time Stamps).
• The `-W lint' option to provide source code and run time error and portability checking (see section Command Line Options).
• The `-W compat' option to turn off these extensions (see section Command Line Options).
• The `-W posix' option for full POSIX compliance (see section Command Line Options).

Version 2.14 of gawk introduced these features:

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

Version 2.15 of gawk introduced these features:

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

Version 3.0 of gawk introduced these features:

• The next file statement became nextfile (see section The nextfile Statement).
• The `--lint-old' option to warn about constructs that are not available in the original Version 7 Unix version of awk (see section Major Changes between V7 and SVR3.1).
• The `--traditional' option was added as a better name for `--compat' (see section Command Line Options).
• The ability for FS to be a null string, and for the third argument to split to be the null string (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 RT variable (see section How Input is Split into Records).
• The gensub function for more powerful text manipulation (see section Built-in Functions for String Manipulation).
• The strftime function acquired a default time format, allowing it to be called with no arguments (see section Functions for Dealing with Time Stamps).
• Full support for both POSIX and GNU regexps (see section Regular Expressions).
• The `--re-interval' option to provide interval expressions in regexps (see section Regular Expression Operators).
• IGNORECASE changed, now applying to string comparison as well as regexp operations (see section Case-sensitivity in Matching).
• The `-m' option and the fflush function from the Bell Labs research version of awk (see section Command Line Options; also see section Built-in Functions for Input/Output).
• The use of GNU Autoconf to control the configuration process (see section Compiling gawk for Unix).
• Amiga support (see section Installing gawk on an Amiga).

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