REXX Scripting

Module 1: Introduction to REXX Scripting

Lesson 1: Overview of REXX Scripting

History and Evolution of REXX

REXX (Restructured Extended Executor) was designed in the late 1970s by Michael Cowlishaw at IBM. It was developed as a high-level programming language to provide both ease of use for beginners and advanced functionality for experienced developers. REXX gained popularity due to its simplicity and was integrated into IBM’s VM/CMS and later z/OS systems.

Key milestones in REXX history include:

1980: Initial release of REXX as a part of the VM/SP system.
1984: Introduction of REXX as an official IBM product.
1990s: Expansion into OS/2, Windows, and other operating systems.
2004: Adoption of Open Object REXX (ooREXX) as an open-source project.

REXX remains relevant in modern mainframe environments, especially for task automation, data processing, and scripting within z/OS.

Key Features and Advantages

REXX’s design emphasizes simplicity, readability, and flexibility, making it suitable for a wide range of applications. Some key features include:

Human-Readable Syntax: Designed to be readable and easy to learn, reducing the barrier for entry.
Powerful String Manipulation: Built-in functions for parsing, searching, and manipulating text.
Platform Independence: REXX can run on various systems, from mainframes to personal computers.
Integration with z/OS: Provides robust capabilities for scripting, job automation, and system interaction.
Error Handling: Built-in support for trapping and managing errors during execution.

Advantages of using REXX in a z/OS COBOL environment include:

Seamless integration with TSO/E (Time Sharing Option Extensions) and ISPF (Interactive System Productivity Facility).
Rapid development and prototyping capabilities.
Simplified debugging and testing processes.

Basic Syntax and Structure of REXX

A REXX program consists of statements, commands, and functions. The language’s structure is straightforward, enabling both beginner and advanced users to write efficient scripts.

Example: Basic REXX Program

/* REXX Script: Hello World */
say "Hello, World!"
exit

Variables and Data Types:

Variables in REXX are typeless, holding any type of data (numeric or string).
Example:

name = "John"
age = 25
say "Name:" name "Age:" age

Control Structures:

Conditional Statements:

if age > 18 then
    say "Adult"
else
    say "Minor"

Loops:

do i = 1 to 5
    say "Iteration:" i
end

Functions and Procedures:

REXX provides a wide range of built-in functions and supports user-defined functions. Example:

result = length("REXX scripting")
say "The length is:" result

By understanding these basic elements, users can begin leveraging REXX for scripting and automation in z/OS environments.

Lesson 2: Understanding zOS COBOL Environment

Introduction to zOS Architecture

z/OS is IBM’s flagship operating system for mainframes, designed for enterprise-level computing. It supports high-volume transaction processing, batch jobs, and extensive data handling capabilities. Key components of z/OS architecture include:

Multi-processing Capabilities: z/OS supports parallel processing and is designed for high reliability and scalability.
Time Sharing Option (TSO): Enables multiple users to access the system concurrently.
Interactive System Productivity Facility (ISPF): Provides tools for managing datasets, developing applications, and system monitoring.
JES (Job Entry Subsystem): Manages job scheduling, execution, and output processing.

z/OS is structured around datasets, which store everything from user data to program code. Its hierarchical storage management (HSM) system ensures optimal use of storage resources.

Role of COBOL in Mainframe Systems

COBOL (Common Business-Oriented Language) has been the backbone of business computing for decades. It excels in handling data-intensive tasks, making it ideal for industries such as banking, insurance, and retail. Key aspects of COBOL’s role include:

Batch and Transaction Processing: COBOL is optimized for large-scale batch jobs and online transaction processing (OLTP).
Integration with Legacy Systems: Most legacy applications are built in COBOL, making it critical for maintaining and modernizing older systems.
High-Performance Data Processing: COBOL’s capabilities for handling large datasets make it indispensable for mainframe applications.

In the z/OS environment, COBOL interacts seamlessly with other components like DB2 (databases), CICS (transaction processing), and MQ (messaging). Its ongoing relevance stems from the need to maintain and extend existing systems.

Integration of REXX with COBOL

REXX and COBOL complement each other in the z/OS environment, enabling automation, debugging, and task simplification. Integration techniques include:

Data Exchange Between REXX and COBOL:
COBOL programs can invoke REXX scripts for tasks like data preprocessing and reporting.
REXX can pass parameters to COBOL programs and retrieve results.
Debugging and Testing:
REXX scripts can be used to test COBOL modules, simulate input data, and analyze program output.
Automating COBOL Workflows:
REXX can automate job submission (JCL generation), log monitoring, and output processing.

Example:

/* REXX Script to Submit a COBOL Job */
jobname = "COBOLJOB"
address tso "SUBMIT 'USER.COBOL.JCL("jobname")'"
say "Job" jobname "submitted successfully."

Integration of REXX with COBOL enhances productivity by reducing manual effort and providing tools for efficient debugging and testing. Leveraging both technologies ensures a robust and agile z/OS application development environment.

Module 2: Getting Started with REXX on zOS

Lesson 1: REXX Syntax and Basic Commands

Variables and Data Types

REXX variables are dynamic and typeless, meaning they can hold strings or numbers without requiring explicit type declaration.

Key Characteristics:

Variables are case-insensitive.
No type declaration is needed; REXX automatically interprets the type based on context.

Examples:

/* Variable declaration */
name = "Alice"
age = 30

/* Using variables */
say "Name:" name
say "Age:" age

/* Variable reassignment */
age = age + 1
say "Updated Age:" age

Numeric operations are straightforward, with REXX interpreting numbers directly:

x = 5
y = 10
z = x + y
say "Sum:" z

String manipulation is another powerful feature:

text = "Hello, REXX!"
say "Uppercase:" translate(text, 'ABCDEFGHIJKLMNOPQRSTUVWXYZ', 'abcdefghijklmnopqrstuvwxyz')

Control Structures: Loops and Conditionals

REXX offers intuitive control structures to handle decision-making and iterations.

Conditional Statements:

/* If-Else Example */
age = 20
if age >= 18 then
    say "You are an adult."
else
    say "You are a minor."

Select-Cases:

/* Select Example */
choice = "B"
select
    when choice = "A" then say "Option A selected."
    when choice = "B" then say "Option B selected."
    otherwise say "Invalid choice."
end

Loops:

Do Loops: Used for fixed or conditional iterations.

/* Simple Do Loop */
do i = 1 to 5
    say "Iteration:" i
end

/* Conditional Loop */
count = 0
do while count < 3
    count = count + 1
    say "Count:" count
end

Built-in Functions and Procedures

REXX includes an extensive set of built-in functions for operations on strings, numbers, and more.

Common Built-In Functions:

String Functions: - length(string) - Returns the length of a string. - substr(string, start, length) - Extracts a substring. - translate(string) - Converts characters in a string.

text = "REXX scripting"
say "Length:" length(text)
say "Substring:" substr(text, 1, 4)
say "Uppercase:" translate(text, 'ABCDEFGHIJKLMNOPQRSTUVWXYZ', 'abcdefghijklmnopqrstuvwxyz')

Numeric Functions: - abs(number) - Returns the absolute value. - max(number1, number2, …) - Finds the maximum value. - min(number1, number2, …) - Finds the minimum value.

num1 = -10
num2 = 5
say "Absolute:" abs(num1)
say "Maximum:" max(num1, num2)
say "Minimum:" min(num1, num2)

Date and Time Functions: - date(format) - Returns the current date. - time(format) - Returns the current time.

say "Today's Date:" date("S")
say "Current Time:" time("L")

User-Defined Procedures: Users can create reusable procedures for modular scripting.

/* Procedure Example */
say "Starting program"
call greet "Alice"
exit

greet: procedure
    parse arg name
    say "Hello," name "!"
return

These fundamental concepts of REXX scripting enable efficient and powerful automation in z/OS environments.

Lesson 2: Setting Up Your Environment

Installing and Configuring REXX

To begin using REXX in a z/OS environment, you need to ensure the software is properly installed and configured. The steps are as follows:

Verify REXX Availability: - On z/OS, REXX is typically included as part of the TSO/E environment. Verify its presence by executing the following command in TSO: ` TSO REXX` - If unavailable, consult your system administrator to install the required REXX libraries.

Configure the REXX Environment: - Edit the SYSEXEC or SYSPROC dataset to include the library containing your REXX scripts. - Use the following command to allocate a dataset for REXX scripts dynamically:

   allocate dataset('USER.REXX.SCRIPTS') file(sysproc) shr

Ensure the dataset is part of your search path.

Install Additional Tools (Optional): - Tools like IBM Workload Scheduler or ISPF panels enhance REXX usability. - Consider enabling debugging tools, such as TRACE.

Accessing the TSO/E Environment

The TSO/E (Time Sharing Option Extensions) environment is critical for running REXX scripts on z/OS.

Login to TSO/E: - Access the mainframe using your preferred terminal emulator (e.g., TN3270 or IBM Personal Communications). - Enter your credentials to log in.

Verify Access to TSO/E Commands: - Use basic commands like LISTCAT to confirm access. - Allocate datasets for testing REXX:

   allocate dataset('USER.REXX.TEST') file(test) new space(5,5) unit(sysda)

Set Up ISPF Panels: - Launch ISPF to access a user-friendly interface for managing datasets and executing commands. - Navigate to the ISPF Command Shell to execute REXX scripts.

Writing and Executing Your First REXX Script

Once your environment is set up, you can create and execute your first REXX script.

Create the Script: - Open a dataset for editing using ISPF or TSO commands. - Enter the following basic REXX script to display "Hello, World!":

   /* REXX Script: Hello World */
   say "Hello, World!"
   exit

Save and Exit: - Save the script with a .REXX extension in your allocated dataset.

Execute the Script: - Use the EXEC command in TSO: ` exec 'USER.REXX.TEST(HELLO)'` - Alternatively, use the TSO command: ` TSO HELLO`

Debugging Your Script: - Use the TRACE command to debug: rexx trace r say "Debugging started." - Monitor script execution and identify errors.

Setting up the environment is crucial for efficient REXX scripting. Ensure all components are correctly configured to maximize productivity in z/OS.

Module 3: Introduction to REXX Scripting

Lesson 1: Interfacing REXX with COBOL

Passing Data Between REXX and COBOL Programs

REXX and COBOL can exchange data efficiently in a z/OS environment, enabling automation and enhanced functionality.

Techniques for Passing Data:

Via JCL (Job Control Language):
- REXX scripts can dynamically generate JCL to pass parameters to COBOL programs.
- Example:

   /* REXX Script to Pass Parameters via JCL */
   parm1 = "DATA1"
   parm2 = "DATA2"
   address tso
   "ALLOC F(JCLFILE) DSN('USER.JCL.LIBRARY') SHR"
   "EXECIO 0 DISKW JCLFILE (OPEN"
   "EXECIO * DISKW JCLFILE (STEM jcl.)"
   jcl.1 = "//STEP1 EXEC PGM=COBOLPGM,PARM='" parm1 "," parm2 "'"
   jcl.0 = 1
   "EXECIO 0 DISKW JCLFILE (CLOSE"
   "FREE F(JCLFILE)"

Through Temporary Storage (TSQ): - COBOL writes data to a temporary queue, which REXX can read. - Use APIs or commands to manage TSQ data.

Dataset Exchange: - COBOL writes output to a dataset, which REXX reads for further processing.

Example of Using Datasets for Exchange:

COBOL writes to USER.DATA.OUTPUT: cobol WRITE DATA-RECORD FROM 'COBOL OUTPUT DATA'.
REXX reads the dataset:

   "ALLOC F(INFILE) DSN('USER.DATA.OUTPUT') SHR"
   "EXECIO * DISKR INFILE (STEM data.)"

Using REXX for COBOL Program Debugging

REXX can simplify debugging COBOL programs by automating test data generation and monitoring outputs.

Techniques:

Automated Test Data Creation: - REXX scripts can generate large datasets or simulate specific test cases.

   /* REXX Test Data Generator */
   do i = 1 to 100
       data.i = "TESTDATA" || i
   end
   "ALLOC F(TESTDS) DSN('USER.TEST.DATA') NEW SPACE(5,5) UNIT(SYSDA)"
   "EXECIO" 100 "DISKW TESTDS (STEM data.)"

Log Parsing and Analysis: - REXX can analyze COBOL logs for errors or anomalies.

   /* REXX Log Analyzer */
   "ALLOC F(LOGDS) DSN('USER.COBOL.LOG') SHR"
   "EXECIO * DISKR LOGDS (STEM log.)"
   do i = 1 to log.0
       if pos("ERROR", log.i) > 0 then say "Error Found: " log.i
   end

Dynamic Execution Tracing: - Combine REXX with system commands to trace execution paths or variable states.

Case Studies: Practical Examples of Integration

Case Study: Automating Job Submission and Monitoring

Objective: Automate COBOL job execution and monitor results.
Solution: A REXX script submits a COBOL program via JCL, waits for completion, and analyzes output.

   /* REXX Job Submission and Monitoring */
   job = "COBOLJOB"
   address tso "SUBMIT 'USER.JCL.LIBRARY(" job ")'"
   "SDSF STATUS (" job ")"
   "ALLOC F(OUTPUT) DSN('USER.COBOL.OUTPUT') SHR"
   "EXECIO * DISKR OUTPUT (STEM out.)"
   do i = 1 to out.0
       if pos("SUCCESS", out.i) > 0 then
           say "Job completed successfully."
   end

Case Study: Simplified Data Transformation

Objective: Transform input data for COBOL processing using REXX.
Solution: Use REXX to preprocess raw data into a format that COBOL can handle.

Case Study: Debugging Multi-Step COBOL Workflows

Objective: Identify and resolve errors in a multi-step COBOL batch job.
Solution: A REXX script identifies error points by analyzing intermediate files and log outputs.

By combining REXX’s scripting capabilities with COBOL’s robust data processing, developers can streamline workflows, enhance debugging efficiency, and enable automation across mainframe environments.

Lesson 2: File Handling in REXX

Reading and Writing Datasets

REXX provides powerful capabilities to interact with datasets in z/OS. These include reading from and writing to sequential files and PDS members.

Reading a Dataset: Use the EXECIO command to read data into a stem variable:

/* REXX Script: Reading a Dataset */
address tso
"ALLOC F(INFILE) DSN('USER.DATA.INPUT') SHR"
"EXECIO * DISKR INFILE (STEM input.)"
"FREE F(INFILE)"

do i = 1 to input.0
    say input.i
end

Key Notes:
input.0 contains the number of lines read.
input.i holds individual lines.

Writing to a Dataset: You can write data to a dataset using EXECIO:

/* REXX Script: Writing to a Dataset */
address tso
"ALLOC F(OUTFILE) DSN('USER.DATA.OUTPUT') SHR"
output.1 = "This is the first line."
output.2 = "This is the second line."
output.0 = 2

"EXECIO" output.0 "DISKW OUTFILE (STEM output.)"
"FREE F(OUTFILE)"

Working with VSAM Files

REXX can also handle VSAM files, though this requires additional configuration or utilities like IDCAMS or external programs.

Reading a VSAM File Using IDCAMS:

/* REXX Script: Reading a VSAM File */
address tso
"ALLOC F(VSAMFILE) DSN('USER.VSAM.DATASET') SHR"
"EXECIO * DISKR VSAMFILE (STEM vsamData.)"
"FREE F(VSAMFILE)"

do i = 1 to vsamData.0
    say vsamData.i
end

Writing to a VSAM File: To write data to a VSAM file, you typically need to use COBOL or assembler programs. However, REXX scripts can be integrated to prepare or manipulate input data.

Error Handling and Debugging

Proper error handling is crucial for robust REXX scripts. Use built-in debugging commands and error traps.

Error Handling with SIGNAL: The SIGNAL command can catch and handle errors gracefully:

/* Error Handling Example */
signal on syntax
say "Starting script."
"ALLOC F(NONEXISTENT) DSN('MISSING.FILE') SHR"
say "Allocation complete."
exit

syntax:
say "An error occurred during allocation."
exit

Debugging with TRACE: The TRACE command helps in analyzing script execution:

/* Debugging Example */
trace R
say "Debugging started."
a = 10 / 0 /* Intentional error */

TRACE R: Displays each statement before execution.
TRACE I: Provides detailed information about variable values.

Tips for Effective Debugging: - Always use say statements to verify variable values. - Use signal on for unexpected error scenarios.

By mastering file handling techniques and implementing error handling, you can build efficient and reliable REXX scripts in z/OS environments.

Module 4: REXX Automation and Tools

Lesson 1: Automating Tasks with REXX

Batch Processing and Job Submission

REXX excels in automating batch processing tasks and submitting jobs to the mainframe system.

Automating JCL Submission: REXX can dynamically create and submit JCL to run batch jobs.

/* REXX Script for Job Submission */
jobname = "MYJOB"
address tso
"ALLOC F(JCLDS) DSN('USER.JCL.LIBRARY') SHR"
"EXECIO * DISKR JCLDS(" jobname ") STEM joblines."
do i = 1 to joblines.0
    say joblines.i
end
"SUBMIT 'USER.JCL.LIBRARY(" jobname ")'"

Monitoring Job Completion: REXX can track job execution status using SDSF commands or JES output processing.

/* REXX Job Monitoring */
address tso
"SUBMIT 'USER.JCL.LIBRARY(MYJOB)'"
"WAIT 5" /* Pause to allow job execution */
"STATUS 'MYJOB'" /* Check job status */

Automating System Monitoring

System monitoring is a critical aspect of mainframe management, and REXX scripts can simplify this process.

Monitoring System Logs: REXX can parse system logs and highlight issues or anomalies.

/* System Log Monitor */
address tso
"ALLOC F(LOGDS) DSN('SYS1.LOG') SHR"
"EXECIO * DISKR LOGDS (STEM logs.)"
do i = 1 to logs.0
    if pos("ERROR", logs.i) > 0 then
        say "Error Found: " logs.i
end
"FREE F(LOGDS)"

Resource Utilization Tracking: REXX scripts can monitor CPU usage, memory consumption, or dataset utilization.

/* Resource Utilization Tracker */
address tso
"DISPLAY CPU"
"DISPLAY MEM"

Alert Notifications: REXX can integrate with email or messaging systems to send alerts when predefined conditions are met.

/* Alert Example */
if system_status = "DOWN" then
    address tso "SEND EMAIL TO SYSADMIN WITH 'ALERT: SYSTEM DOWN'"

Scheduling Tasks Using REXX Scripts

Scheduling repetitive tasks can be achieved using REXX in conjunction with scheduling utilities or custom scripts.

Creating Scheduled Tasks: REXX can interact with system schedulers like IBM Workload Scheduler (IWS) or run as a cron-like script.

/* Scheduled REXX Task */
call schedule_task 'REXXSCRIPT', 'EVERY HOUR'
exit

schedule_task: procedure
    parse arg scriptname interval
    say "Scheduling task:" scriptname "to run" interval
    /* Logic to integrate with scheduler */
return

Triggering Tasks on Events: Use REXX to set up event-driven task execution, such as processing files upon arrival.

/* Event-Driven Task */
do forever
    if file_exists('USER.DATA.INPUT') then do
        call process_file 'USER.DATA.INPUT'
        exit
    end
    wait 10 /* Check every 10 seconds */
end

Batch Scheduling with Custom Logic: Combine REXX with batch processing to run tasks in specific sequences or under certain conditions.

/* Conditional Batch Scheduling */
if day = "FRIDAY" then
    call run_end_week_tasks
else
    call run_daily_tasks
return

By automating repetitive and critical tasks, REXX significantly enhances system efficiency and reduces manual effort in mainframe environments.

Lesson 2: Tools and Extensions for REXX

Exploring REXX Libraries

REXX libraries provide pre-built functionality, enabling developers to save time and streamline scripting tasks.

Commonly Used Libraries:

SYSEXEC and SYSPROC: - Default REXX libraries in z/OS. - Store frequently used REXX scripts for reuse across the system. - Example:

   /* Allocate SYSEXEC for custom scripts */
   allocate dataset('USER.SYSEXEC.LIB') file(sysproc) shr

ISPF REXX Services: - Enhance script interaction with ISPF panels. - Provide functions for panel customization, file manipulation, and system commands.

   /* Example: Using ISPF Services */
   "ISPEXEC SELECT CMD(EDIT DATASET('USER.DATA.INPUT'))"

External REXX Libraries: - Third-party libraries extend functionality with custom APIs for database access, HTTP calls, and more.

Benefits of REXX Libraries: - Simplified maintenance with centralized script storage. - Reusability across multiple users and applications. - Extended capabilities through specialized APIs.

Using ISPF and SDSF Commands with REXX

ISPF (Interactive System Productivity Facility) and SDSF (System Display and Search Facility) integrate seamlessly with REXX, enabling powerful system management.

ISPF Commands: - Automate ISPF panel navigation and dataset operations.

/* ISPF Navigation Example */
"ISPEXEC SELECT PANEL(ISRUDL)"
"ISPEXEC LMDLIST LVL(USER.DATA)"

Customize ISPF panels for user interaction:

/* Custom ISPF Panel Interaction */
"ISPEXEC ADDPOPUP TITLE('Confirm Action')"

SDSF Commands: - Automate job monitoring and spool management:

/* SDSF Command Example */
"ISFEXEC STATUS"
do i = 1 to isfdata.0
    say "Job:" isfdata.i
end

Extract specific job details:

/* Extract Job Output */
"ISFEXEC SELECT ST(*) OWNER(*)"
do i = 1 to isfout.0
    say "Output Line:" isfout.i
end

Combining ISPF and SDSF with REXX: - Streamline complex workflows by combining dataset management (ISPF) with job monitoring (SDSF).

Integration with Modern Tools and APIs

REXX adapts to modern requirements by integrating with tools and APIs for expanded functionality.

Database Interaction: - REXX can access databases like DB2 using embedded SQL or external APIs.

/* REXX DB2 Example */
address TSO "RUN SQL SELECT * FROM EMPLOYEES WHERE AGE > 30"

HTTP and REST API Calls: - Integrate with web services using HTTP requests via external tools like CURL or native APIs.

/* REST API Example */
"ADDRESS TSO CURL -X GET https://api.example.com/data"

Mainframe Modernization: - Use REXX to bridge legacy COBOL applications with modern technologies (e.g., JSON, XML).

Tool Integration: IBM Workload Scheduler (IWS): - Schedule and monitor batch jobs directly from REXX scripts.

   /* Schedule a Job in IWS */
   "IWS SCHEDULE 'USER.JOB(SAMPLEJOB)'"

Automation Tools: - Combine REXX with tools like Ansible or Jenkins for DevOps pipelines.

Example: API Integration for DevOps:

/* Trigger a Jenkins Build */
"ADDRESS TSO CURL -X POST https://jenkins.example.com/build"

Future-Proofing with REXX: - By leveraging modern APIs and tools, REXX remains a vital component of mainframe systems, bridging traditional and contemporary technologies.

Module 5: Case Studies and Practical Exercises

Lesson 1: Hands-On Projects

Developing a COBOL Debugging Tool with REXX

This project involves building a REXX-based debugging tool to streamline COBOL program debugging.

Objective: - Create a REXX script to analyze COBOL program logs, trace execution paths, and identify issues.

Steps:

Log Parsing: - Read and parse COBOL execution logs to extract error messages and runtime data.

   /* REXX Log Parser */
   address tso
   "ALLOC F(LOGDS) DSN('USER.COBOL.LOG') SHR"
   "EXECIO * DISKR LOGDS (STEM loglines.)"
   do i = 1 to loglines.0
       if pos("ERROR", loglines.i) > 0 then
           say "Error Found: " loglines.i
   end
   "FREE F(LOGDS)"

Execution Trace: - Use TRACE and variable tracking to monitor program execution and variable values.

Interactive User Interface: - Develop an ISPF panel for real-time debugging data display.

   "ISPEXEC ADDPOPUP TITLE('Debug Results')"

Outcome: A tool that simplifies COBOL debugging by automating error detection and execution analysis.

Creating a System Monitoring Dashboard

This project focuses on creating a real-time system monitoring dashboard using REXX.

Objective: - Display live data on CPU utilization, memory usage, and dataset status.

Steps: Gather System Metrics: - Use TSO commands to collect system data.

   /* System Metric Collector */
   address tso
   "DISPLAY CPU"
   "DISPLAY MEM"
   "DISPLAY ACTIVE DATASETS"

Data Visualization: - Format and present the collected data in a user-friendly ISPF panel.

   /* ISPF Panel for System Data */
   "ISPEXEC DISPLAY PANEL(SYSDASH)"

Set Up Alerts: - Configure REXX to notify users when thresholds are exceeded (e.g., high CPU usage).

   if cpu_util > 80 then
       say "ALERT: High CPU Usage!"

Outcome: A customizable dashboard for system administrators to monitor mainframe health in real-time.

Implementing a Batch Job Automation System

This project automates batch job submission, monitoring, and reporting.

Objective: - Create a system to submit, monitor, and validate the output of batch jobs.

Steps: Job Submission: - Use REXX to dynamically generate and submit JCL.

   /* REXX Job Submitter */
   jobname = "BATCHJOB"
   address tso
   "ALLOC F(JCLDS) DSN('USER.JCL.LIB') SHR"
   "EXECIO * DISKR JCLDS(" jobname ") STEM joblines."
   "SUBMIT 'USER.JCL.LIB(" jobname ")'"

Monitoring Job Status: - Use SDSF commands to track job execution and capture job output.

   /* Job Monitor */
   "ISFEXEC STATUS"
   do i = 1 to isfdata.0
       say "Job Status:" isfdata.i
   end

Output Validation: - Parse and validate job output to ensure successful execution.

   /* Output Validator */
   "ALLOC F(OUTDS) DSN('USER.OUTPUT.DATA') SHR"
   "EXECIO * DISKR OUTDS (STEM outputlines.)"
   do i = 1 to outputlines.0
       if pos("SUCCESS", outputlines.i) > 0 then
           say "Job Completed Successfully."
   end

Outcome: An automated system that enhances efficiency and reduces manual intervention in batch processing.

These hands-on projects demonstrate practical applications of REXX in mainframe environments, enhancing both development and operations efficiency.

Lesson 2: Real-World Applications

Performance Optimization with REXX

Optimizing the performance of REXX scripts ensures efficient execution in demanding mainframe environments.

Techniques for Optimization: Streamlining Logic: - Minimize redundant operations by consolidating loops and conditions.

   /* Optimized Loop Example */
   do i = 1 to 1000 by 10
       say "Processing batch:" i
   end

Efficient Dataset Handling: - Use bulk operations for dataset reads and writes to reduce overhead.

   /* Bulk Dataset Read */
   "EXECIO * DISKR DATASET (STEM data.)"

Variable Management: - Avoid unnecessary variable assignments and ensure proper cleanup.

   drop unused_variable

Using Built-in Functions: - Replace manual logic with built-in functions for faster execution.

   /* Replace Custom Logic with Built-in Function */
   result = max(value1, value2, value3)

Outcome: Enhanced script performance with reduced execution time and resource usage.

Error Handling and Logging Best Practices

Effective error handling and logging are crucial for robust REXX scripts.

Error Handling: Using SIGNAL for Error Traps: - Implement error traps to catch and respond to runtime errors.

   /* Error Trap Example */
   signal on syntax
   "EXECIO * DISKR MISSING.DATA (STEM data.)"
   exit

   syntax:
   say "Error: Dataset not found."

Validating Inputs: - Ensure all inputs are validated before processing to prevent runtime errors.

   if dataset_name = "" then
       say "Error: Dataset name is missing."

Logging Best Practices:

Centralized Logging: - Write all logs to a central dataset for easier monitoring.

   /* Centralized Log Example */
   "EXECIO 1 DISKW LOGDATA (STEM logline.)"

Structured Log Format: - Use structured formats (e.g., JSON or CSV) for logs to simplify parsing and analysis.

   logline.1 = "{timestamp: '2024-11-20', event: 'JobStart', details: 'Job initiated'}"

Real-Time Monitoring: - Implement real-time log analysis to identify and resolve issues proactively.

Outcome: Improved script reliability and easier debugging through structured error handling and logging.

Case Study: Automating Job Control with REXX

Scenario: A company needs to automate the submission and monitoring of COBOL batch jobs, reducing manual effort and ensuring timely execution.

Solution: Dynamic Job Creation: - Use REXX to dynamically generate JCL based on input parameters.

   /* Dynamic JCL Generation */
   jobname = "AUTOJOB"
   "ALLOC F(JCLDS) DSN('USER.JCL.LIB') SHR"
   jcl.1 = "//"jobname" JOB (ACCT),'AUTOJOB',CLASS=A,MSGCLASS=X"
   jcl.2 = "//STEP1 EXEC PGM=COBOLPGM"
   jcl.0 = 2
   "EXECIO * DISKW JCLDS (STEM jcl.)"

Automated Submission: - Submit the generated JCL and monitor its execution.

   /* Job Submission and Monitoring */
   "SUBMIT 'USER.JCL.LIB(" jobname ")'"
   "SDSF STATUS ('"jobname"')"

Output Validation: - Parse job output to ensure successful execution.

   /* Output Validation */
   "ALLOC F(OUTDS) DSN('USER.OUTPUT') SHR"
   "EXECIO * DISKR OUTDS (STEM output.)"
   do i = 1 to output.0
       if pos("SUCCESS", output.i) > 0 then
           say "Job completed successfully."
   end

Outcome: A robust, automated system for job control that enhances efficiency and reduces operational overhead.