The American Programmer

Learn how to write programs in the REXX language for TSO, MVS, OS/390, Z/os.
My first book on the REXX programming language, is out of print. This is my second book on REXX for TSO.
It improves on REXX in the TSO Environment in every way: it clarifies important points, it is better organized, and gives better examples.
There are very few other books in print about REXX in the TSO Environment.
This book quickly gets you started writing programs in REXX for MVS, OS/390, Z/OS. It covers all REXX language elements, all TSO built-in functions, and the more important built-in functions.

172 pages, 8.5 x 11 inches. Revised. Mailed USPS priority next business day.

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Gabe Gargiulo is the author of several mainframe books:
REXX Quick Reference    
REXX in the TSO Environment (Available new and used)    
The REXX Language on TSO    MVS JCL (Out of Print)
Mastering OS2/REXX (Available new and used)   
ISPF Services: Using the Dialogue Manager, with REXX   
MVS/TSO (Available new and used)

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Table of Contents REXX for TSO Book

Introduction


Chapter 1: Overview of REXX

REXX features

Example of a REXX Program, with explanations 


2: Setting Up to Execute REXX in TSO/ISPF.

1. Create a library

2. Specify details for allocating library

3. Create a member

4. Create the SETUP member in edit

5. Execute the Setup Program

6. Try it


3: The Basic Features

The initial REXX comment

SAY - display on the terminal

Variables

The Literal

The Label

PULL - accept input from the terminal

DO for looping

	Concatenating Data Strings

EXIT to end your program

Passing commands to TSO 

	Short Description of all of REXX's Verbs or Keywords


4: IF

	The simplest form of the IF:

	A few things to think about:

	Comparison operators

	The DO END sequence

	Boolean operators


5: Looping

	The simplest form

	The simple DO...END sequence.

	The DO number ... END sequence

	The DO variable ... END sequence

	The DO that increments a variable

	The DO WHILE

	The DO UNTIL

	The DO FOREVER

	LEAVE

	ITERATE: Skipping back to the top of the loop


6: SELECT: REXX's CASE Structure

	Example

	Points of syntax

	Several instructions: example




7: PARSE

	The basic form of PARSE

	Origins

	The Action of PARSE

	Short forms of PARSE

	Uses of PARSE: ARG

	The ARG in a main program.

	The ARG in a user-written function or subroutine. 

	Uses of PARSE: PULL

	Uses of PARSE: EXTERNAL

	Uses of PARSE: VAR

	Uses of PARSE: VALUE

	Uses of PARSE: SOURCE


8: Debugging

	Interactive Debug

		What you can do during interactive debug

		Turning on Interactive Debug

		Codes displayed during interactive debug

	Tracing: the Smaller Guns 

	Combinations of the TRACE verb


9: Trapping Unexpected Conditions

	Situations you might want to trap

	Trapping Unexpected Conditions: General

		The trap that terminates

		The trap that continues

		Changing the name of the trap

	Trapping Unexpected Conditions: Syntax

	Trapping Unexpected Conditions: Error	

	Trapping Unexpected Conditions: Failure	

	Trapping Unexpected Conditions: Novalue

	Trapping Unexpected Conditions: Halt

	Trapping Unexpected Conditions: Contents of the Trap


10: SIGNAL: the Extinct "GO TO"

	Signal: go there (but don't come back)


11: Math

	When does REXX do math?

	Math: Arithmetic Operators

	Math: Precision


12: Passing Commands to Command Processors

	Passing commands to the environment

	How Do You Get REXX to Pass a Command to a Command

	Processor?

	What Do the Return Codes (RC) mean?

	What Command Processors Are Out There?

	How do You Send Commands to a Command Processor?

		Sending commands to TSO

		Sending commands to ISPF

		Sending commands to the ISPF Editor

	How Does Your Program Know if the Command Processor is There?


13: Built-in Functions

	Some examples 

	Basics of functions

	CALLing a function

	Some of the more important functions. [the more important REXX functions are covered]

	Built-in Functions: TSO Functions


14: Writing Your Own Functions

	Example of Internal Function

	Internal, user-written functions

	What makes a function a function?

Protecting Variables

	Example of External Function

External, user-written functions

Search Order for Functions and Subroutines


15: Writing Your Own Subroutines

	Example

Writing internal subroutines


16: The Internal Data Queue, or Stack

	What is it?

	How do you put things into the data queue?

	Data Queue or terminal dialogue?

	Functions used with the data queue

	Leftovers


17: Compound Variables

	Traditional subscripted variables vs REXX compound variables

	Understanding compound variables

	Examples:


18: Reading and Writing Files: EXECIO

	The Basics.

	The ALLOCATE command for reading. 

	Reading with EXECIO

	Reading whole file with EXECIO into the Data Queue - example

	Reading one record at a time into the Data Queue - example:

	Reading whole file with EXECIO into an array - example

	Additional options for Reading

	The ALLOCATE command for writing. 

	Writing with EXECIO

	Writing whole file from the Data Queue - Example:

	Writing whole file with EXECIO from an array - example


19: The INTERPRET Instruction

	Why INTERPRET?


20: Running REXX in Batch, with JCL

	Example

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Sample Pages (formatting not same as in the book)

(This is a part of the chapter) 11: Math

Math: Precision




If Einstein had had REXX he would have been twice the genius he was. (Or would he have been creating video games...). 
REXX does math to whatever precision you desire, limited only by the amount of computer memory you have available. 
REXX does everything in decimal numbers so you won't see approximate results. 


Changing the precision.

The default precision is 9 digits. If a calculation generates more significant digits than that, 
REXX will round the answer and stop at 9 digits. You can change the precision to 100 or 1000 or 10000! 
On some systems you can go much higher than that. Useful for figuring your income tax.....


To change the precision to 100 digits:

	NUMERIC DIGITS    100   

The following example will show you what that means.

	SAY    2 / 3                  


	/*displays  .666666667 (9 digits)     */

   

	NUMERIC DIGITS    100   


	SAY 2 / 3           

  

	/*displays   

	.6666666666666666666666666666666666666666

	6666666666666666666666666666666666666666

	66666666666666666667    */     


Do Practice Problems 35 - 38.

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15: Writing Your Own Subroutines

Example


/* REXX */

/* instructions */

CALL MYSUB

/* instructions */

/* instructions */

EXIT


MYSUB:

ANSWER = NUM1 + NUM2

SAY ANSWER

RETURN


 

Writing internal subroutines

An internal subroutine is used to simplify coding - to avoid long cumbersome logic structures. I strongly encourage their use. 


A subroutine looks like a function, but it's not a function.

Here are the characteristics of a subroutine:

invoked by: 	CALL subroutine-name 
Example: 		CALL ADDEM 
ARG is optional
RETURN is required but you don't have to pass information back on it
variables are generally shared with the main part of the program
there are no external subroutines in REXX. 

Do Practice Problems 48 - 52.

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Practice problems and suggested answers that go with the book. View as web page     

You can obtain them here. (Ask for REXX, then rexx2.prob.txt) Get code     

REXX Manuals from IBM

TSO Line Mode (Native TSO) commands. (such as DELETE, HRECALL, ALLOCATE, Line Mode EDIT) Essential for REXX and CLIST programmers

Writing ISPF Editor Macros in REXX

More information on setting up to use REXX on TSO

CLIST and REXX

REXX on VM/CMS

My REXX Quick Reference Book

REXX Error Codes 2 Expression > 64000 characters (OS/2 only) 3 Program is unreadable 4 Program interrupted 5 Machine storage exhausted 6 Unmatched /* or quote 7 WHEN or OTHERWISE expected 8 Unexpected THEN or ELSE 9 Unexpected WHEN or OTHERWISE 10 Unexpected or unmatched END 11 Control stack full 12 Clause > 500 characters 13 Invalid character in data 14 Incomplete DO/SELECT/IF 15 Invalid hex constant 16 Label not found 17 Unexpected PROCEDURE 18 THEN expected 19 String or symbol expected 20 Symbol expected 21 Invalid data on end of clause 22 Invalid character string 23 Invalid SBCS/DBCS mixed string 24 Invalid trace request 25 Invalid subkeyword found 26 Invalid whole number 27 Invalid do syntax 28 Invalid LEAVE or ITERATE 29 Environment name too long 30 Name or string > 250 characters 31 Name starts with numeric or "." 32 Invalid use of stem 33 Invalid expression result 34 Logical value not 0 or 1 35 Invalid expression 36 Unmatched "(" in expression 37 Unexpected "," or ")" 38 Invalid template or pattern 39 Evaluation stack overflow 40 Incorrect call to routine 41 Bad arithmetic conversion 42 Arithmetic overflow/underflow 43 Routine not found 44 Function did not return data 45 No data specified on function return 46 Invalid variable reference 47 Unassigned 48 Failure in system service 49 Interpreter failure

This book will get you into programming with Classic REXX (Restructured eXtended eXecutor language) on IBM's mainframe running MVS, OS390 or Zos TSO/ISPF. You can run REXX online during a TSO session, or in a batch program with JCL.
REXX is a user-friendly interpreted scripting language developed by Michael Cowlishaw. It uses clear English-language verbs and parameters.
REXX is used for application prototyping and one-time jobs. REXX is generally interpreted and so there is a performance penalty.
REXX is used as the driver script for developing and running ISPF applications.

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