Extensions in `gawk' not in POSIX `awk'
=======================================

   The GNU implementation, `gawk', adds these features:

   * The `AWKPATH' environment variable for specifying a path search for
     the `-f' command line option (see Invoking `awk': Command Line.).

   * The various `gawk' specific features available via the `-W'
     command line option (see Invoking `awk': Command Line.).

   * The `ARGIND' variable, that tracks the movement of `FILENAME'
     through `ARGV'.  (see Built-in Variables.).

   * The `ERRNO' variable, that contains the system error message when
     `getline' returns -1, or when `close' fails.  (*note Built-in
     Variables::.).

   * The `IGNORECASE' variable and its effects (*note Case-sensitivity
     in Matching: Case-sensitivity.).

   * The `FIELDWIDTHS' variable and its effects (*note Reading
     Fixed-width Data: Constant Size.).

   * The `next file' statement for skipping to the next data file
     (see The `next file' Statement: Next File Statement.).

   * The `systime' and `strftime' built-in functions for obtaining and
     printing time stamps (*note Functions for Dealing with Time
     Stamps: Time Functions.).

   * The `/dev/stdin', `/dev/stdout', `/dev/stderr', and `/dev/fd/N'
     file name interpretation (see Standard I/O Streams: Special Files.).

   * The `-W compat' option to turn off these extensions (
see Invoking `awk': Command Line.).

   * The `-W posix' option for full POSIX compliance (*note Invoking
     `awk': Command Line.).