Mastering REXX Troubleshooting with TRACE: A Comprehensive Guide

Hello, REXX enthusiasts! In this blog post, I will introduce you to REXX TRACE debugging – a powerful tool for troubleshooting and analyzing RE

XX programs. Debugging is an essential skill for writing reliable and efficient scripts, and TRACE helps track program execution step by step. Understanding TRACE levels, from basic instruction tracing to detailed variable evaluation, is crucial for diagnosing errors effectively. I will guide you through different TRACE options, how they influence debugging, and practical examples to enhance your troubleshooting skills. By the end, you’ll gain a solid grasp of using TRACE to debug and optimize your REXX scripts. Let’s dive in!

An Introduction to Using TRACE for Troubleshooting in REXX Programming Language

The TRACE instruction in REXX is a powerful debugging tool that helps developers analyze program execution and identify errors efficiently. It provides real-time insights into how a script runs by displaying statements before or after execution, making troubleshooting easier. TRACE offers multiple modes for debugging. TRACE R (Results) shows expressions before evaluation, while TRACE A (All) displays statements after execution. TRACE I (Intermediate) helps track variable changes, making it useful for detecting logical errors. Additionally, TRACE ? allows conditional tracing by prompting user input before proceeding with execution. By strategically placing TRACE commands in a REXX script, developers can monitor execution flow, identify incorrect values, and pinpoint logic errors without altering the program’s core functionality. Combined with other debugging methods like the SAY statement and error handling (SIGNAL ON ERROR), TRACE enhances script reliability and simplifies debugging in REXX programming.

What is TRACE Used for in Troubleshooting REXX Programs?

When writing scripts in REXX, debugging is an essential process to ensure that the program behaves as expected. One of the most powerful debugging tools in REXX is the TRACE instruction. It helps track program execution, display variable values, and understand the flow of control.

What is TRACE in REXX?

The TRACE instruction prints execution details of your REXX script, helping in debugging. It allows you to:

• Monitor step-by-step execution of the program.
• View variable values after assignments.
• See how expressions are evaluated.
• Detect errors and incorrect logic.

By using TRACE, you can observe each statement executed in the order it runs and view how expressions and variables change over time.

When to Use TRACE in REXX?

Use Case	Recommended TRACE Option
Debugging all statements	TRACE A
Checking command-line execution	TRACE C
Finding error locations	TRACE E
Debugging expressions	TRACE I
Viewing only results	TRACE R
Step-by-step debugging	TRACE ?
Controlling trace depth	TRACE number

Syntax of TRACE

TRACE [option]

Where option specifies how much detail you want. The options include:

• TRACE O → Turns tracing off.
• TRACE A → Traces all statements, showing program execution.
• TRACE C → Traces only command-line instructions (useful for external commands).
• TRACE E → Traces only errors.
• TRACE I → Traces intermediate expressions, showing step-by-step evaluation.
• TRACE L → Traces label processing.
• TRACE N → Traces normal execution (default mode).
• TRACE R → Traces only results of expressions.
• TRACE ? → Enables interactive debugging (pauses after each step).
• TRACE number → Sets tracing depth level (useful for loops and nested execution).

In-Depth Explanation with Examples

An in-depth explanation of TRACE in REXX, covering all options with detailed examples, debugging techniques, and best practices.

Example 1: Using TRACE A (Full Execution Trace)

/* REXX program demonstrating TRACE A */
TRACE A
say "Starting execution..."
x = 10
y = 5
sum = x + y
say "Sum is:" sum

Output:

>>>    1 *-* say "Starting execution..."
       +++     "Starting execution..."
Starting execution...
>>>    2 *-* x = 10
>>>    3 *-* y = 5
>>>    4 *-* sum = x + y
>>>    5 *-* say "Sum is:" sum
       +++     "Sum is: 15"
Sum is: 15

• >>> Indicates the line being executed.
• +++ Displays the evaluated result of expressions inside say.
• TRACE A shows each instruction as it executes.

Example 2: Using TRACE I (Step-by-Step Expression Evaluation)

/* Demonstrate TRACE I for intermediate values */
TRACE I
a = 4
b = 2
c = (a + b) * 3
say "Final result:" c

Output:

>>>    1 *-* a = 4
>>>    2 *-* b = 2
>>>    3 *-* c = (a + b) * 3
       >I>      (4+2)*3 -> 6*3 -> 18
>>>    4 *-* say "Final result:" c
       +++     "Final result: 18"
Final result: 18

• TRACE I shows intermediate calculations.
• The output breaks down c = (a + b) * 3 step by step.

Example 3: Using TRACE R (Result Tracking Only)

TRACE R
num1 = 15
num2 = 7
diff = num1 - num2
say "Difference is:" diff

Output:

>>>    1 *-* num1 = 15
>>>    2 *-* num2 = 7
>>>    3 *-* diff = num1 - num2
       >R>      8
>>>    4 *-* say "Difference is:" diff
       +++     "Difference is: 8"
Difference is: 8

• >R> shows only computed results of expressions.
• It hides unnecessary program flow details but helps check correctness of calculations.

Example 4: Using TRACE ? (Interactive Debugging)

TRACE ?
x = 10
y = 5
result = x * y
say "Multiplication result:" result

Execution Flow:

>>>    1 *-* x = 10
Press ENTER to continue...
>>>    2 *-* y = 5
Press ENTER to continue...
>>>    3 *-* result = x * y
Press ENTER to continue...
>>>    4 *-* say "Multiplication result:" result
       +++     "Multiplication result: 50"
Multiplication result: 50

• TRACE ? pauses execution after each statement.
• The user presses ENTER to continue or modifies variables.

Example 5: Using TRACE E for Error Debugging

TRACE E
num = "ten" /* Incorrect data type */
sum = num + 5 /* This will cause an error */
say "Sum is:" sum

Output:

>>>    1 *-* num = "ten"
>>>    2 *-* sum = num + 5
       Error 40: Incorrect use of data

• TRACE E triggers tracing only when an error occurs.
• Helps identify exactly where the error happened.

Why is TRACE Needed for Troubleshooting in REXX ?

The TRACE instruction in REXX is an essential tool for debugging and troubleshooting. It helps programmers understand program flow, identify errors, and analyze variable values. Below are the key reasons why TRACE is necessary for troubleshooting in REXX.

1. Understanding Program Execution

When a REXX script runs, it executes instructions sequentially. However, complex logic, loops, and conditionals can make tracking execution difficult. TRACE helps by displaying each line as it executes, allowing developers to see how the program flows and ensuring it follows the expected logic.

2. Identifying Logical Errors

Logical errors occur when a program does not produce the expected output, even if there are no syntax errors. By using TRACE A or TRACE I, developers can analyze how expressions are evaluated step by step, making it easier to spot incorrect calculations or misused conditions.

3. Debugging Variable Assignments

Sometimes, unexpected results occur due to incorrect variable values. TRACE R helps by showing only the final computed results, allowing programmers to verify whether variables hold the expected values and helping track unintended modifications.

4. Detecting Incorrect Data Types

REXX treats variables dynamically, meaning a string can accidentally be used where a number is expected. Using TRACE E (error tracing), developers can quickly identify and resolve type mismatches, ensuring correct data handling.

5. Troubleshooting Expression Evaluation

Complex expressions can lead to incorrect results due to misinterpretation of mathematical precedence. TRACE I helps by breaking down expressions into smaller steps, showing how REXX evaluates each part, making it easier to verify calculations.

6. Finding the Source of Errors

Errors such as division by zero or uninitialized variables can crash a program. TRACE E helps pinpoint the exact location where an error occurs, reducing the time spent searching for the issue.

7. Monitoring Loop Execution

Loops are critical for automation, but errors like infinite loops or incorrect loop counters can occur. TRACE A helps by displaying each iteration, allowing programmers to check whether the loop is executing as expected.

8. Tracking Conditional Statements

IF-THEN-ELSE logic can sometimes behave unexpectedly due to incorrect conditions. Using TRACE ?, developers can execute one statement at a time, verifying that the correct path is followed in conditional branching.

9. Debugging External Command Execution

When executing system commands in REXX using ADDRESS, debugging can be difficult. TRACE C allows developers to trace only command-line executions, helping troubleshoot external command failures.

10. Interactive Debugging with User Control

Sometimes, stopping execution at each step helps diagnose issues in real-time. TRACE ? enables interactive debugging, where execution pauses after each step, allowing programmers to modify variables and test different values.

Example of Using TRACE for Troubleshooting in REXX Programming Language

Debugging is an essential part of programming, and in REXX, the TRACE instruction is a powerful tool for troubleshooting errors, tracking variable values, and understanding the flow of execution. In this detailed guide, we will explore multiple examples using TRACE in different scenarios to identify and fix issues in REXX programs.

Example 1: Debugging a Simple Arithmetic Error with TRACE A

Problem:

A user writes a script to calculate the total cost of products but gets an incorrect result.

Code with Issue:

/* REXX script to calculate total cost */
cost_per_item = 50
quantity = "five"   /* Mistakenly assigned a string instead of a number */
total_cost = cost_per_item * quantity
say "Total cost is:" total_cost

Using TRACE to Debug

Add TRACE A at the beginning to track execution.

TRACE A
cost_per_item = 50
quantity = "five"
total_cost = cost_per_item * quantity
say "Total cost is:" total_cost

Output:

>>>    1 *-* cost_per_item = 50
>>>    2 *-* quantity = "five"
>>>    3 *-* total_cost = cost_per_item * quantity
       Error 40: Incorrect use of data

Analysis and Fix:

• The problem is quantity = "five" instead of quantity = 5.
• REXX treats "five" as a string and fails when multiplying with cost_per_item.
• Fix by changing quantity = 5.

Corrected Code:

TRACE A
cost_per_item = 50
quantity = 5  /* Corrected */
total_cost = cost_per_item * quantity
say "Total cost is:" total_cost

Output (After Fix):

>>>    1 *-* cost_per_item = 50
>>>    2 *-* quantity = 5
>>>    3 *-* total_cost = cost_per_item * quantity
>>>    4 *-* say "Total cost is:" total_cost
       +++     "Total cost is: 250"
Total cost is: 250

Example 2: Debugging Conditional Statements with TRACE I

Problem:

A script checks if a number is positive, negative, or zero, but always returns incorrect output.

Code with Issue:

num = -5
if num > 0 then
    say "Number is positive"
else if num < 0 then
    say "Number is negative"
else
    say "Number is zero"

Using TRACE I to Debug Expression Evaluation

TRACE I
num = -5
if num > 0 then
    say "Number is positive"
else if num < 0 then
    say "Number is negative"
else
    say "Number is zero"

Output:

>>>    1 *-* num = -5
>>>    2 *-* if num > 0 then
       >I>      -5>0 -> 0
>>>    3 *-* else if num < 0 then
       >I>      -5<0 -> 1
>>>    4 *-* say "Number is negative"
       +++     "Number is negative"
Number is negative

Analysis:

• TRACE I shows the condition evaluation.
• num > 0 evaluates to 0 (false).
• num < 0 evaluates to 1 (true), so the correct branch executes.

Fix (No Fix Needed, but Good Debugging Practice)

This confirms the script is working correctly.

Example 3: Debugging Loops with TRACE R

Problem:

A loop to calculate the sum of the first 5 numbers gives the wrong output.

Code with Issue:

sum = 0
do i = 1 to 5
    sum = sum + i
end
say "Total sum:" sum

Using TRACE R to Debug

TRACE R
sum = 0
do i = 1 to 5
    sum = sum + i
end
say "Total sum:" sum

Output:

>>>    1 *-* sum = 0
>>>    2 *-* do i = 1 to 5
>>>    3 *-* sum = sum + i
       >R>      1
>>>    3 *-* sum = sum + i
       >R>      3
>>>    3 *-* sum = sum + i
       >R>      6
>>>    3 *-* sum = sum + i
       >R>      10
>>>    3 *-* sum = sum + i
       >R>      15
>>>    5 *-* say "Total sum:" sum
       +++     "Total sum: 15"
Total sum: 15

Analysis:

• TRACE R shows the updated value of sum at each iteration.
• The loop executes correctly, adding 1 + 2 + 3 + 4 + 5 = 15.

Fix (No Fix Needed, but Good Debugging Practice)

This confirms the loop runs correctly.

Example 4: Finding Errors in External Command Execution with TRACE C

Problem:

A script tries to list directory contents but fails.

Code with Issue:

ADDRESS SYSTEM "dir"
say "Command executed."

Using TRACE C to Debug

TRACE C
ADDRESS SYSTEM "dir"
say "Command executed."

Output (If there’s an error):

>>>    1 *-* ADDRESS SYSTEM "dir"
       Error 97: Command execution failure

Analysis and Fix:

• The error suggests the dir command failed.
• Possible fixes:
  • Check if the dir command is valid for the system (use ls for Linux).
  • Ensure the script has proper permissions.

Fixed Code (For Linux Users)

TRACE C
ADDRESS SYSTEM "ls"
say "Command executed."

Example 5: Interactive Debugging with TRACE ?

Problem:

A complex script behaves unexpectedly, and we want to check execution step by step.

Using TRACE ?

TRACE ?
x = 10
y = 2
result = x / y
say "Result is:" result

Output (Pauses Execution Step by Step):

>>>    1 *-* x = 10
Press ENTER to continue...
>>>    2 *-* y = 2
Press ENTER to continue...
>>>    3 *-* result = x / y
Press ENTER to continue...
>>>    4 *-* say "Result is:" result
       +++     "Result is: 5"
Result is: 5

Analysis:

• TRACE ? pauses execution after each statement.
• The user can check variable values before continuing.

Best Use Case:

• Useful when debugging a complex script interactively.
• Helps catch issues before they affect the entire script.

Advantages of Using TRACE for Troubleshooting in REXX Programming Language

Here are the advantages of using TRACE for troubleshooting in REXX programming language:

1. Step-by-Step Execution for Easy Debugging: The TRACE command allows developers to execute scripts line by line, helping them identify errors and understand the program flow in a structured manner.
2. Multiple TRACE Modes for Detailed Analysis: REXX provides different TRACE levels (TRACE R, TRACE I, TRACE C, etc.), allowing developers to control the depth of debugging information based on their needs.
3. Immediate Visibility of Variable Values: Using TRACE R mode, developers can see variable assignments in real time, making it easier to track data changes and identify incorrect values.
4. Helps in Detecting Logical Errors: Since TRACE displays each executed line, developers can analyze logic mistakes, such as incorrect loops, faulty conditions, or unexpected branches in the code.
5. No Need for External Debugging Tools: Unlike other programming languages that require specialized debugging software, REXX’s built-in TRACE command provides sufficient debugging capabilities without additional tools.
6. Interactive Debugging with PAUSE Option: The TRACE ? command allows users to pause script execution after each statement, giving them time to analyze outputs and manually control the debugging process.
7. Works in Both Command Line and Mainframe Environments: The TRACE command is supported across platforms, making it useful for debugging REXX scripts in both mainframe (TSO, ISPF) and non-mainframe (Windows, Linux) environments.
8. Assists in Troubleshooting External Program Calls: By tracing script execution, developers can pinpoint where errors occur when calling external programs or system commands from a REXX script.
9. Lightweight and Easy to Use: Unlike advanced debugging tools that require setup and configuration, TRACE is a simple and lightweight command that can be activated instantly within a script.
10. Enhances Script Maintainability and Reliability: Regularly using TRACE during development helps detect and fix issues early, leading to more reliable and maintainable REXX scripts for automation and processing tasks.

Disadvantages of Using TRACE for Troubleshooting in REXX Programming Language

Here are the disadvantages of using TRACE for troubleshooting in REXX programming language:

1. Generates Excessive Output for Large Scripts: When debugging long or complex scripts, TRACE can produce an overwhelming amount of output, making it difficult to pinpoint specific issues.
2. Lacks Graphical Debugging Features: Unlike modern debugging tools with breakpoints, variable watches, and interactive stepping, TRACE provides only text-based output, limiting its usability for complex debugging tasks.
3. Cannot Directly Modify Variable Values During Execution: Unlike advanced debugging environments where variables can be altered on the fly, TRACE only displays values without allowing modifications, making iterative debugging harder.
4. Requires Manual Analysis of Execution Flow: Since TRACE simply logs the execution process, developers must manually inspect output to identify errors, which can be time-consuming and inefficient for large scripts.
5. Difficult to Debug Multi-Threaded or Parallel Processes: TRACE is primarily designed for linear execution, making it ineffective for debugging scripts involving concurrent processes or parallel execution.
6. Not Suitable for Debugging External System Calls: When a script interacts with external programs or system commands, TRACE does not always capture detailed error messages, making troubleshooting such interactions difficult.
7. Can Slow Down Script Execution: Enabling TRACE significantly impacts performance, as each command and variable change is logged, making execution slower, especially in loops or iterative processes.
8. Lack of Persistent Debugging Logs: TRACE output is typically displayed on the console and does not provide built-in mechanisms for structured logging, requiring developers to manually redirect output to files for later analysis.
9. No Conditional Breakpoints or Advanced Debugging Features: Unlike modern debuggers that allow setting conditional breakpoints, TRACE lacks finer control, forcing developers to manually add checks or modify scripts to debug specific sections.
10. Can Be Confusing for Beginners: Understanding and effectively using different TRACE modes (TRACE R, TRACE I, TRACE C, etc.) requires familiarity with REXX’s debugging process, making it less intuitive for new programmers.

Future Development and Enhancement of Using TRACE for Troubleshooting in REXX Programming Language

Here are the future developments and enhancements that could improve using TRACE for troubleshooting in REXX programming language:

1. Graphical Debugging Interface: Developing a GUI-based debugger for REXX that integrates TRACE with interactive features like breakpoints, call stack visualization, and variable watches would enhance debugging efficiency.
2. Support for Conditional Breakpoints: Introducing the ability to set breakpoints based on conditions (e.g., stop execution when a variable reaches a certain value) would reduce excessive TRACE output and improve targeted debugging.
3. Enhanced Logging Capabilities: Allowing TRACE outputs to be logged into structured files with timestamps, log levels, and categorized error reporting would improve post-execution analysis and debugging.
4. Integration with Modern IDEs: Extending TRACE functionality to integrate with editors like VS Code or Eclipse with syntax highlighting, real-time debugging insights, and variable monitoring would make REXX debugging more user-friendly.
5. Step-by-Step Execution with Inline Variable Modification: Enhancing TRACE to allow real-time modification of variable values during script execution would enable more interactive and dynamic debugging.
6. Performance Optimization for Large Scripts: Optimizing TRACE to selectively trace only specific parts of the script (e.g., functions, loops, or error-prone sections) instead of generating excessive output for the entire script would improve efficiency.
7. Improved Debugging for External System Calls: Enhancing TRACE to capture detailed logs when interacting with external programs or system commands would make it easier to debug automation scripts involving OS-level interactions.
8. Parallel Debugging for Multi-Threaded Processes: Future enhancements could introduce TRACE support for multi-threaded or concurrent REXX execution, allowing developers to debug parallel scripts more effectively.
9. Auto-Analysis and Debugging Suggestions: Implementing AI-powered debugging assistance that analyzes TRACE output and suggests potential causes of errors or incorrect logic would help developers debug faster.
10. User-Friendly Debugging Commands: Simplifying TRACE command usage by introducing easy-to-understand debugging functions (e.g., DEBUG ON, DEBUG OFF) instead of multiple TRACE modes (TRACE R, TRACE I, etc.) would make troubleshooting more accessible to beginners.