Arnold D. Robbins, AWK Language Programming — Preface (1996)
“ In 1985 a new version made the programming language more powerful, introducing user-defined functions, multiple input streams, and computed regular expressions. This new version became generally available with Unix System V Release 3.1. The version in System V Release 4 added some new features and also cleaned up the behavior in some of the "dark corners" of the language. The specification for awk in the POSIX Command Language and Utilities standard further clarified the language based on feedback from both the gawk designers, and the original Bell Labs awk designers. ”
