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Major Changes Between V7 and SVR3.1

The @command{awk} language evolved considerably between the release of Version 7 Unix (1978) and the new version that was first made generally available in System V Release 3.1 (1987). This minor node summarizes the changes, with cross-references to further details:

• The requirement for `;' to separate rules on a line (@pxref{Statements/Lines, ,@command{awk} Statements Versus Lines}).
• User-defined functions and the return statement (see section User-Defined Functions).
• The delete statement (see section The delete Statement).
• The do-while statement (see section The do-while Statement).
• The built-in functions atan2, cos, sin, rand, and srand (see section Numeric Functions).
• The built-in functions gsub, sub, and match (see section String Manipulation Functions).
• The built-in functions close and system (see section Input/Output Functions).
• The ARGC, ARGV, FNR, RLENGTH, RSTART, and SUBSEP built-in variables (see section Built-in Variables).
• The conditional expression using the ternary operator `?:' (see section Conditional Expressions).
• The exponentiation operator `^' (see section Arithmetic Operators) and its assignment operator form `^=' (see section Assignment Expressions).
• C-compatible operator precedence, which breaks some old @command{awk} programs (see section Operator Precedence (How Operators Nest)).
• Regexps as the value of FS (see section Specifying How Fields Are Separated) and as the third argument to the split function (see section String Manipulation Functions).
• Dynamic regexps as operands of the `~' and `!~' operators (see section How to Use Regular Expressions).
• The escape sequences `\b', `\f', and `\r' (see section Escape Sequences). (Some vendors have updated their old versions of @command{awk} to recognize `\b', `\f', and `\r', but this is not something you can rely on.)
• Redirection of input for the getline function (see section Explicit Input with getline).
• Multiple BEGIN and END rules (see section The BEGIN and END Special Patterns).
• Multidimensional arrays (see section Multidimensional Arrays).

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