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 Statements/Lines).
• User-defined functions and the return statement (see User-defined).
• The delete statement (see Delete).
• The do-while statement (see Do Statement).
• The built-in functions atan2(), cos(), sin(), rand(), and srand() (see Numeric Functions).
• The built-in functions gsub(), sub(), and match() (see String Functions).
• The built-in functions close() and system() (see I/O Functions).
• The ARGC, ARGV, FNR, RLENGTH, RSTART, and SUBSEP built-in variables (see Built-in Variables).
• Assignable $0 (see Changing Fields).
• The conditional expression using the ternary operator ‘?:’ (see Conditional Exp).
• The expression ‘index-variable in array’ outside of for statements (see Reference to Elements).
• The exponentiation operator ‘^’ (see Arithmetic Ops) and its assignment operator form ‘^=’ (see Assignment Ops).
• C-compatible operator precedence, which breaks some old awk programs (see Precedence).
• Regexps as the value of FS (see Field Separators) and as the third argument to the split() function (see String Functions), rather than using only the first character of FS.
• Dynamic regexps as operands of the ‘~’ and ‘!~’ operators (see Regexp Usage).
• The escape sequences ‘\b’, ‘\f’, and ‘\r’ (see 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 Getline).
• Multiple BEGIN and END rules (see BEGIN/END).
• Multidimensional arrays (see Multi-dimensional).