Rexx

REXX, short for Restructured Extended Executor, is a small, interpreted scripting language designed for readability and rapid development. It was created by IBM programmer Mike Cowlishaw in the late 1970s for IBM systems, notably CMS and TSO/E, to provide a simple, English-like syntax that could be learned quickly and used for batch processing, data extraction, and automation. REXX emphasizes clarity, flexibility, and portability.

Its syntax is procedural and dynamically typed. Programs use procedures and variables without declarations. Core control structures include IF/THEN/ELSE, DO loops, and SELECT..WHEN. Built-in functions cover string and file handling (LENGTH, SUBSTR, WORD, POS) and a PARSE facility to extract data. The ADDRESS statement directs commands to the host environment or external programs, enabling cross-platform scripting. Variables are scalar or stem (array-like) variables that grow as needed.

Notable implementations include Regina Rexx (open-source, cross-platform), IBM's Object REXX (ooREXX), and NetRexx for the Java platform. IBM also provided TSO/E Rexx for mainframes, and various commercial and academic variants exist for other environments.

Today, REXX persists in legacy mainframe batch jobs and automation tasks, and is valued for readability and rapid text processing. Its clear syntax influenced later scripting languages, and multiple implementations continue to be maintained by communities and vendors.