Changes between S5R3.1 and S5R4
===============================

   The System V Release 4 version of Unix `awk' added these features
(some of which originated in `gawk'):

   * The `ENVIRON' variable (see Built-in Variables.).

   * Multiple `-f' options on the command line (see Invoking `awk': Command Line.).

   * The `-v' option for assigning variables before program execution
     begins (see Invoking `awk': Command Line.).

   * The `--' option for terminating command line options.

   * The `\a', `\v', and `\x' escape sequences (*note Constant
     Expressions: Constants.).

   * A defined return value for the `srand' built-in function (
see Numeric Built-in Functions: Numeric Functions.).

   * The `toupper' and `tolower' built-in string functions for case
     translation (see Built-in Functions for String Manipulation: String Functions.).

   * A cleaner specification for the `%c' format-control letter in the
     `printf' function (*note Using `printf' Statements for Fancier
     Printing: Printf.).

   * The ability to dynamically pass the field width and precision
     (`"%*.*d"') in the argument list of the `printf' function (
see Using `printf' Statements for Fancier Printing: Printf.).

   * The use of constant regexps such as `/foo/' as expressions, where
     they are equivalent to use of the matching operator, as in `$0 ~
     /foo/' (see Constant Expressions: Constants.).