Introduction to Mainframe Scripting Languages | by Zubair Idris Aweda | Jul, 2026 | MediumSitemapOpen in appSign up<br>Sign in

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Introduction to Mainframe Scripting Languages

Automating the Machine’s Everyday Work

Zubair Idris Aweda

10 min read·<br>3 days ago

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In part one of this series, we looked at the programming languages that power a mainframe’s core business logic, COBOL, PL/I, HLASM, Java, Python, and Go, and how they combine to run the applications an organisation actually depends on. But writing that logic is only half the story. Someone still has to submit the jobs that run it, manage the datasets it reads and writes, and stitch together the dozens of small operational tasks that keep a mainframe environment running smoothly day to day. That’s where scripting languages come in.<br>This article picks up exactly where part one left off. We’ll briefly recap the difference between programming and scripting languages in a mainframe context, then look closely at the scripting languages you’re most likely to encounter as a new mainframer: REXX, CLIST, and the UNIX shell scripting available through UNIX System Services. As before, we’ll look at examples and typical use cases for each.<br>You should be familiar with what a mainframe is, and how it works, and reading part one of this series first will give you useful context for what follows.<br>A Quick Recap: Programming vs. Scripting<br>As covered in part one, programming languages on the mainframe are generally compiled, rigorously tested, and used to build large, standalone applications, the kind that calculate interest, validate claims, or process millions of transactions a day. Scripting languages, by contrast, are typically interpreted, quicker to write and modify, and used to automate tasks, manage datasets, and orchestrate the work that programs and jobs do, rather than implement complex business logic themselves.<br>This split matters practically, not just conceptually. If you need to reliably process a bank’s overnight transaction volume with strict error handling, you write that in COBOL. If you need to check whether a dataset exists, back it up if it does, and kick off a job that processes it, a REXX script is usually the far more sensible tool, faster to write, faster to change, and perfectly suited to a task that doesn’t need the same rigour as core business logic.<br>With that distinction fresh in mind, let’s look at the scripting languages themselves.<br>REXX: The Mainframe’s Automation Workhorse<br>REXX (RE structured eX tended eX ecutor) is, without much competition, the most widely used scripting language on z/OS. Developed by IBM in the early 1980s, REXX was designed to be easy to read and write, with a syntax that feels closer to plain English than most programming languages, while still being powerful enough to handle genuinely complex automation tasks.<br>REXX scripts, often called “execs”, can be run directly from TSO/E, from within ISPF, or invoked from other REXX programs and even some system exits. A simple REXX exec might look like this:<br>/* REXX */<br>SAY 'Enter your name:'<br>PULL NAME<br>SAY 'Hello, ' NAME '! Welcome to the mainframe.'Notice how close this reads to natural language: SAY displays output, PULL reads input, and the whole thing runs without needing to declare variable types or worry about memory management. That readability is a large part of why REXX became so popular so quickly.<br>REXX earns its keep on real systems by doing things like:<br>Automating repetitive ISPF tasks, such as searching through hundreds of members in a partitioned dataset for a particular string<br>Manipulating datasets, copying, comparing, renaming, and reorganising them based on conditions<br>Acting as glue code between different applications and utilities, calling one program, checking its output, and deciding what to do next<br>Building simple interactive tools and menus for other mainframe users, often wrapped in an ISPF panel for a friendlier interface<br>A slightly more realistic example, one that checks whether a dataset exists before doing anything with it, might look like this:<br>/* REXX */<br>ADDRESS TSO<br>"LISTDS 'ZUBAIR.TEST.DATA'"<br>IF RC = 0 THEN<br>SAY 'Dataset exists, proceeding...'<br>ELSE<br>SAY 'Dataset not found, exiting.'Here, ADDRESS TSO tells REXX to send the following command to TSO for execution, and RC captures the return code from that command, a pattern you'll see constantly in real REXX scripts, since so much of mainframe automation revolves around running a command and reacting to whether it succeeded.<br>REXX also handles loops and conditional logic comfortably, which is what allows it to scale from small one-off utilities to genuinely substantial automation tools. Here’s a slightly longer example that loops through a list of dataset names, checking each one:<br>/* REXX */<br>DSNAMES = "ZUBAIR.DATA1 ZUBAIR.DATA2 ZUBAIR.DATA3"<br>DO I = 1 TO WORDS(DSNAMES)<br>DSN = WORD(DSNAMES,...