Major Changes between V7 and S5R3.1
===================================

   The `awk' language evolved considerably between the release of
Version 7 Unix (1978) and the new version first made widely available in
System V Release 3.1 (1987).  This section summarizes the changes, with
cross-references to further details.

   * The requirement for `;' to separate rules on a line (*note `awk'
     Statements versus Lines: Statements/Lines.).

   * User-defined functions, and the `return' statement (
see User-defined Functions: User-defined.).

   * The `delete' statement (see The `delete' Statement: Delete.).

   * The `do'-`while' statement (see The `do'-`while' Statement: Do Statement.).

   * The built-in functions `atan2', `cos', `sin', `rand' and `srand'
     (see Numeric Built-in Functions: Numeric Functions.).

   * The built-in functions `gsub', `sub', and `match' (*note Built-in
     Functions for String Manipulation: String Functions.).

   * The built-in functions `close', which closes an open file, and
     `system', which allows the user to execute operating system
     commands (see Built-in Functions for Input/Output: I/O Functions.).

   * The `ARGC', `ARGV', `FNR', `RLENGTH', `RSTART', and `SUBSEP'
     built-in variables (see Built-in Variables.).

   * The conditional expression using the operators `?' and `:' (
see Conditional Expressions: Conditional Exp.).

   * The exponentiation operator `^' (see Arithmetic Operators: Arithmetic Ops.) and its assignment operator form `^=' (*note
     Assignment Expressions: Assignment Ops.).

   * C-compatible operator precedence, which breaks some old `awk'
     programs (see Operator Precedence (How Operators Nest): Precedence.).

   * Regexps as the value of `FS' (*note Specifying how Fields are
     Separated: Field Separators.), and as the third argument to the
     `split' function (*note Built-in Functions for String
     Manipulation: String Functions.).

   * Dynamic regexps as operands of the `~' and `!~' operators (
see How to Use Regular Expressions: Regexp Usage.).

   * Escape sequences (see Constant Expressions: Constants.) in
     regexps.

   * The escape sequences `\b', `\f', and `\r' (*note Constant
     Expressions: Constants.).

   * Redirection of input for the `getline' function (*note Explicit
     Input with `getline': Getline.).

   * Multiple `BEGIN' and `END' rules (*note `BEGIN' and `END' Special
     Patterns: BEGIN/END.).

   * Simulated multi-dimensional arrays (*note Multi-dimensional
     Arrays: Multi-dimensional.).