1. Free Rexx ! Everything You Ever Wanted to Know
About Rexx (but were afraid to ask)
Howard Fosdick
(C) 2005 FCI

2. Who Am I? Independent consultant DBA / SA for: Oracle, DB2, SQL Server
Linux, Unix, Windows
Founder IDUG, MWDUG, CAMP
Author: Rexx Programmer’s Reference
Contact:

3. Viewpoint / Purpose All languages have their strengths & roles
Not here to “put down” other languages
Here to present Rexx’s strengths and
discuss where it fits in your toolbox
(1) Know where Rexx fits
(2) Teach you to script it in < 2 hours !
Goals:

4. Outline
Why Scripting ?
Why Rexx ?
Rexx Tutorial
Further Info

5. I. Why Scripting ?

6. Ka-Boom! 2 Big Software Trends Converge Free and Open Source Scripting
Perl,
Python,
Rexx,
Tcl/Tk,
Bash,
Korn,
Ruby,
others
Java,
C/C++,
COBOL
Visual Basic,
VBScript,
WSH

7. What’s a Scripting Language ?
Rexx:
General purpose
Free / open source
Universal
Portable code
Transferable skills
Standardized
(8 of 9 free Rexxes meet stds)
Dynamic
Sizing (variables & arrays)
Memory management
No “variable declarations”
No “data typing”
Integrated debugger
Interpreted
High-level
Glue language

8. Scripting Vs. Traditional Languages
-- Lower level
-- Compiled
-- More detail-oriented
-- Manual variable management
-- Pre-declared variables
-- More programmer effort
-- “Coding” languages
-- Optimize execution speed
-- High level
-- Interpretive
-- More productive
-- Varying degrees of
automatic variable management
-- Shifts burden to the machine
-- “Glue” languages
-- Acceptable execution speed
Rexx, Perl, Python,
Tcl/Tk, Ruby, others
C/C++, COBOL,
Java, Pascal, others

9. When to Use Rexx Yes No -- Productivity -- Reliability
-- Quick development
-- Glue language
-- Prototyping
-- Systems administration
-- OS extensions
-- Portable apps
-- Mainframe migrations
-- Embedded programming
-- Handhelds
-- Text processing
-- Interactive development /
debugging
-- Optimal execution speed
is required
-- Systems -level programming
(No BIOS interrupts, direct
addressing, etc.)

10. Performance Ratio of compiler to interpreter
speed remains constant while
processor speeds increase
exponentially
200k
10k 4k 70
Year
Mhz ghz
CPU PII PIV

11. II. Why Rexx ?

12. “Easy but Powerful” “Easy but Powerful”
Why Rexx Vs Other Scripting Languages ?
“Easy but Powerful”
“Easy but Powerful”
Ease of use benefits experienced developers ...
FAST coding !
Reliable code
Easy to code right out of memory
Maintainable code
70%+ of IT does maintenance
This determines your code’s longevity
Saves your company $$$

13. Rexx uses specific technologies to tie them together
Why Rexx Vs Other Scripting Languages ?
Power
Simplicity
Conflict !
Rexx uses specific technologies to tie them together

14. Power Through Simplicity by…
Small instruction set, w/ power in the functions
Extensible
Call external functions just like internal
Glue language (uses OS commands, interfaces,
DLLs, shared libraries, services, objects, etc.)
Minimal syntax
Minimal special characters, variables, etc.
Automated memory management
Automated variable management
No data definitions
No data typing
Dynamic array sizes
Dynamic string or variable lengths

15. Rexx presents a unique scripting paradigm. Power Through Simplicity…
Rexx presents a radically different philosophy on how to achieve power than the “Unix tradition” languages (Perl, Bash, Korn, Awk, etc.)
Rexx presents a unique
scripting paradigm.

16. The Language Structure Makes Rexx Easy
Operators
Arithmetic
Comparison
Logical
String
2 dozen Instructions
Learn from
the inside out
70 Built-in
Functions
Other Features
OS commands, external functions, DLLs, APIs, widgets, etc.

17. Rexx Runs Everywhere… Rexx predominates on systems in red
Linux-- all versions
Unix-- all versions
BSD-- all versions
Windows-- all versions
Mac OS-- all versions
DOS all versions (32- and 16- bit)
Handhelds-- Windows CE, Palm OS, Symbian/EPOC32
Embedded-- Embedded Linux, DOS, Windows variants
Mainframes-- OS, VM, VSE (all versions)
IBM mid-range-- i5/OS, OS/400 (all versions)
Many others-- Amiga OS, AROS, OpenVMS, BeOS,
OpenEdition, AtheOS/Syllable, SkyOS,
QNX (QNX4/QNX6), OS/2, eCS, osFree, more…
Rexx predominates on systems in red

18. The Free Rexx Interpreters
BRexx
Regina
Rexx/imc
All major
operating systems
Windows, DOS (32/16 bit),
Windows CE, Linux, Unix,
Mac OS, others
Unix, Linux, BSD
Rexx for
Palm OS
Reginald r4
Windows
Windows
Palm OS
Open Object
Rexx
OOP
extensions
roo!
NetRexx
Linux, Windows,
Solaris, AIX
Any Java
Environment
Windows

19. Rexx Free Tools and Interfaces
Over 100 free tools for Rexx. Examples:
SQL database access
GUIs
XML
Web programming
Math libraries
Regular Expressions
Code managers
Communications functions
OS interface libraries
Graphics
Speech, MIDI, sound
. . . you name it . . .

20. III. Let’s Code !

21. Example Script # 1…
/*******************************************************************/
/* Find Payments: */
/* Reads accounts lines one by one, and displays overdue */
/* payments (lines containing the phrase PAYMENT_OVERDUE). */
arg filein /* Read the input file name*/
do while lines(filein) > /* Do while a line to read */
input_line = linein(filein) /* Read an input line */
if pos('PAYMENT_OVERDUE',input_line) > 0 then
say 'Found it:' input_line /* Write line if $ overdue */
end

22. Simplicity in this script…
Minimal syntax
Minimal special characters and variables
Free format
Use spaces & blank lines however desired
Case-insensitive (capitalize however you want)
No explicit file definition
File is automatically OPEN’ed and CLOSE’d
Automatic “declaration” of variables
(see FILEIN and INPUT_LINE)
No “data typing”
All variables are strings
Numbers are strings that look like numbers
Decimal arithmetic (portable, consistent results)
Automatic conversions where sensible

23. What is “Power” ? Power is not solving the problem in the fewest LOC!
Is it the number of Lines of Code (LOC) ?
Can reduce LOC by nesting functions
But why write a complex “fortune-cookie” script ?
Power is not solving the problem in the fewest LOC!
Power is a deft script that solves the problem
in a reliable, readable, maintainable manner

24. Example Script # 2… This script does the same thing as Example #1
arg filein
fgrep PAYMENT_OVERDUE filein
This script does the same thing as Example #1

25. The Power of Glue Languages
Rexx evaluates a statement, sends anything
that is not Rexx to the “external environment”
(by default this is the OS)
Full power of a string-manipulation language
to direct external interfaces
Inspect return code, command output, messages,
and respond
Rexx is a glue language

26. Structured Control InstructionsIf
If then else
Do End
Do While
Select
Call
(case)
Subroutine
or Function

27. Un-Structured Control Instructions
Do Until
Do Forever
Iterate
Leave
Signal
(goto)

28. Rexx Functions… 70 Built-in Functions:
String manipulation (character, bit, hex)
Word manipulation
I/O
Numeric
Environmental
Conversion
Other
2 statements access external function library
Those functions are then coded just like built-ins

29. Example Script # 3…
/*******************************************************************/
/* Code Lookup: */
/* Looks up the area code for the town the user enters */
area. = '' /* Initialize array entries to null */
area.CHICAGO = /* Define a table of area codes */
area.HOMEWOOD = 708
area.EVANSTON = 847
do while town <> '' /* Loop until user enters null line */
say 'For which town do you want the area code?'
pull town
if town <> '' then do
if area.town = ''
then say 'Town' town 'is not in my database'
else say 'The area code for' town 'is' area.town
end

30. Simplicity in this script…
Array recognized by the period (area.)
Do not have to declare arrays or predefine their size
Sets all possible elements to null string (area. = ‘’)
Subscript array by any arbitrary string
(content-addressable memory or associative memory)
Arrays can be:
Dense or sparse
Contain homogenous or heterogeneous elements
Represent records or C structs
Expand to size of memory
Automatic capitalization (pull & array element names)
Can always override Rexx’s automation

31. Example Script # 4… (part I) /* Find Books: */
/* This program illustrates how arrays may be of any dimension */
/* in retrieving book titles based on their keyword weightings. */
keyword. = '' /* Initialize both arrays to all null strings */
title. = ''
/* The array of keywords to search for among the book descriptors */
keyword.1 = 'earth' ; keyword.2 = 'computers'
keyword.3 = 'life' ; keyword.4 = 'environment'
/* The array of book titles, each having several descriptors */
title.1 = 'Saving Planet Earth'
title.1.1 = 'earth'
title.1.2 = 'environment'
title.1.3 = 'life'
title.2 = 'Computer Lifeforms'
title.2.1 = 'life'
title.2.2 = 'computers'
title.2.3 = 'intelligence'
title.3 = 'Algorithmic Insanity'
title.3.1 = 'computers'
title.3.2 = 'algorithms'
title.3.3 = 'programming'

32. Example Script # 4… (part II)
arg weight /* Get number keyword matches required for retrieval */
say 'For weight of' weight 'retrieved titles are:' /* Output header */
do j = 1 while title.j <> '' /* Look at each book */
count = 0
do k = 1 while keyword.k <> '' /* Inspect its keywords */
do l = 1 while title.j.l <> '' /* Compute its weight */
if keyword.k = title.j.l then count = count + 1
end
if count >= weight then /* Display titles matching the criteria */
say title.j

33. Discussion Array keyword. is a lookup table or list
key/value pairs like Perl or Berkeley DB
Array title. is a tree
Trees can be balanced or not
DO I = 1 TO n BY m WHILE condition FOR x
DO UNTIL …
DO FOREVER
DO n
IF condition THEN DO
. . .
END
ELSE DO DO IF
Enclose multiple statements
within a DO END pair

34. Create Any Data Structure With Rexx Arrays :
Element 1
Key Value 1
b.1
b.1.1
b.1.1.1
b.1.1.2
b.2
b.2.1
b.2.2
b.2.3
b.3
b3.1
b.3.1.1 b
Key Value 2
Element 2
Key Value 3
Element 3
Key Value 4
A Simple List
or Look-up Table
Key-value Pairs
b.1
b.1.1
b.1.2
b.2
b.2.1
b.2.2
b.3
b.3.1
b.3.2
b.1
b.1.1
b.2
b.2.1
b.2.2
b.2.3
b.3
b.4
A Multi-level Tree
(unbalanced)
Also: linked list, doubly
linked list, stack, queue,
dequeue, etc...
Balanced Tree
Un-Balanced Tree

35. Example-- Creating a Linked List
list.0 = HEAD ; list.0.next = /* Define linked list. */
list.1 = 'a' ; list.1.next = /* You could also */
list.2 = 'b' ; list.2.next = /* create it */
list.3 = TAIL ; list.3.next = TAIL /* dynamically */
call display_linked_list /* Display the linked list */
list.99 = 'after a, before b' /* Add new item in list */
list.99.next = /* Point new item to next */
list.1.next = /* Point to the new item */
exit
display_linked_list: /* Displays the linked list*/
sub = 0
do while list.sub.next <> TAIL
say 'Element:' list.sub
sub = list.sub.next
end
return

36. Why Rexx Vs Other Scripting Languages ?
For a language that “lacks data structures,” Rexx sure has a lot of them!
Power thru Simplicity

37. IV. More about Rexx

38. Rexx Standards 8 of 9 free Rexx interpreters adhere to TRL-2
Extensions
TRL-2
ANSI
8 of 9 free Rexx interpreters adhere to TRL-2
ANSI adds little beyond TRL-2
Most Rexxes offer extensions
Extensions offer OS-specific stuff and other niceties

39. Rexx Standards Early 90s 1990 1996 1985 TRL-1 TRL-2 SAA ANSI Language
Level
3.50
4.00
5.00

40. The Evolution of Rexx Object-oriented Rexx Standard or “Classic” Rexx
Early 1980s
Mid 1990s
Standard or “Classic” Rexx
NetRexx
(for Java
environments)

41. Rexx on Handhelds Native DOS Emulation Interpreter: Interpreter:
Windows CE BRexx
Palm OS Rexx for Palm OS
Symbian / EPOC Regina
PocketDOS
XTM
others
BRexx
+ Integrates with...
+ DOS Services
+ DOS Applications
+ Many DOS apps
instantly available
without any changes
+ Faster
+ Integrates with native services

42. How DOS Emulation Works
Rexx Scripts
Rexx Interpreter
DOS Operating System
DOS Emulator
Native operating system
Each layer
runs on top
of the one
below it
PC Hardware

43. Object-Oriented Rexx Means…
Classic Rexx
Classes and Methods
PLUS
Inheritance & Derivation
Encapsulation
Abstraction
Polymorphism
Huge Class Library

44. Object Rexx Adds to Classic Rexx . . .
Classes and
Methods
Complete Object
Orientation
Object
Rexx
Built-in Objects,
Special Variables,
many other features
New Instructions
And Much More
More Functions
New Operators

45. NetRexx A “Rexx-like” language
Brings Rexx ease of use to Java environment
NetRexx scripts use Java classes
Script:
Classes for use by Java
Applets
Applications
Servlets
Java Beans (EJBs)
Client & server side both

46. NetRexx Goes Beyond Classic Rexx…
Java environment integration
Object orientation
New instructions
Changed
and Extended
with . . .
Data typing (“types”)
Indexed strings
Special names
Special methods
… and much more …

47. Developing and Running NetRexx Scripts
To translate, compile and run in one step enter: nrc -run hello
Translate NetRexx source
into a Java program
Class file
Eg: hello.class
Source script
Eg: hello.nrx
Java file
Eg: hello.java
Compile Java into bytecode
Run
NetRexx interprets and/or compiles. Can generate commented,
formatted Java code. Runs under JVM or stand-alone.

48. V. More Rexx Features

49. How Rexx Supports Modularity Modularity Internal Routines External
Resources
-- Extensions and
Function Libraries
-- Operating System Commands
-- Commands to other environments
-- External Programs
-- API Interfaces to external features
-- API into Rexx
-- Built-in Functions
-- Functions you develop
-- Subroutines

50. String Processing Operations
abc abc
abcabc
Concatenation
Joins two or more strings
abcabc
Bifurcation
Splits a string
abc abc
abcabc
Parsing
Scans and analyzes a string, may split it into
its constituent components
Parse Count = 2
abcdef
Pattern Matching
Identifies patterns in strings
Find “def”

51. Parsing Operations By Words Separate by words By Pattern
Separate , using , commas
By Numeric
Pattern
abc abc abc
Columns:

52. The Two I/O Modes Line-oriented Process one line at a time
Character-oriented
Process one character at a time
linein
charin
charout
lineout
lines
chars
+ More portable
+ Reads “special” characters

53. The Stack is both a Stack and a Queue
PULL,
PARSE PULL
PUSH
QUEUE
Rexx’s Stack is a generalized communications mechanism

54. Rexx Supports Recursion
Script X
How
Recursion
Works
Yes
End Test
Fufilled ? No
Call
Script X

55. Tip – Steps to Good Programming Style
Ect !
Error checking
Structured Code
Modularity
Comments
Limit Nesting
Spacing & indentation
Good variable names
Capitalization

56. Debugging Options SAY Instruction TRACE Instruction in batch mode
Interactive TRACE
+ Quick, informal
+ Great for simple problems
+ Requires changing code
(adding SAY instructions)
+ Resolves challenging problems
+ Allows real-time code tests
+ Programmer-directed
interaction resolves problems
+ Quick & easy, but powerful
+ Batch script trace
+ Can set trace level based on user input
+ Many trace settings available
+ Good for “paperanalysis” of a problem

57. Condition / Exception Trapping
signal on condition name label_name
…code of the main routine...
label_name:
…code of the error handling routine...
Conditions: error, failure, halt, novalue, notready, syntax, lostdigits

58. VI. Conclusions

59. Conclusions Trends ! Free & open source languages have taken over
Scripting is the “quiet revolution”
Rexx offers “Power through Simplicity”
Useful addition to your toolbox

60. Resources Next... Rexx Programmer’s Reference at Amazon
INTERPRETER: DOWNLOAD:
Regina
BRexx
Reginald
Rexx/imc
Rexx for Palm OS r4
roo!
Open Object Rexx
NetRexx
Rexx Programmer’s Reference at Amazon
     

61. ? ? ? ? ?
questions... ? ? ? ?