A.1 Major Changes Between V7 and SVR3.1

The 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 section summarizes the changes, with cross-references to further details:

• The requirement for ‘;’ to separate rules on a line (see section 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).
• Assignable $0 (see section Changing the Contents of a Field).
• The conditional expression using the ternary operator ‘?:’ (see section Conditional Expressions).
• The expression ‘index-variable in array’ outside of for statements (see section Referring to an Array Element).
• The exponentiation operator ‘^’ (see section Arithmetic Operators) and its assignment operator form ‘^=’ (see section Assignment Expressions).
• C-compatible operator precedence, which breaks some old 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), rather than using only the first character of FS.
• 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 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).