SVR4 (The GNU Awk User’s Guide)

The System V Release 4 (1989) version of Unix awk added these features (some of which originated in gawk):

The ENVIRON array (see section Predefined Variables)
Multiple -f options on the command line (see section Command-Line Options)
The -v option for assigning variables before program execution begins (see section Command-Line Options)
The -- signal for terminating command-line options
The ‘\a’, ‘\v’, and ‘\x’ escape sequences (see section Escape Sequences)
A defined return value for the srand() built-in function (see section Numeric Functions)
The toupper() and tolower() built-in string functions for case translation (see section String-Manipulation Functions)
A cleaner specification for the ‘%c’ format-control letter in the printf function (see section Format-Control Letters)
The ability to dynamically pass the field width and precision ("%*.*d") in the argument list of printf and sprintf() (see section Format-Control Letters)
The use of regexp constants, such as /foo/, as expressions, where they are equivalent to using the matching operator, as in ‘$0 ~ /foo/’ (see section Using Regular Expression Constants)
Processing of escape sequences inside command-line variable assignments (see section Assigning Variables on the Command Line)