Rexx Overview

7/14/2019 Rexx Overview

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Howard Fosdick(C) 2006 FCI

Free Rexx ! Everything You Ever Wanted to Know

About Rexx (but were afraid to ask)

Version 2.0



Who Am I?

• Presentation by Howard Fosdick,

author of Rexx Programmer’s Reference

• Find the book at www. Amazon.com/rexx

• This presentation is published under the OpenPublication License (OPL).



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:



Outline

1. Why Scripting ?2. Why Rexx ?3. Rexx Tutorial4. Further Info



I. Why Scrip t ing ?



2 Big Software Trends Converge

Ka-Boom!

Free andOpen Source

Scripting

Perl,Python,Rexx, Tcl/Tk,Bash,Korn,Ruby,others

Java,C/C++,

COBOL Visual Basic,VBScript,

WSH



• Interpreted

• High-level

• Glue language

• 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” • Inte rated debu er

Rexx:

What‟s a Scr ipt ing Language ?



Scripting Vs. Traditional Languages

-- High level

-- Interpretive-- More productive-- Varying degrees of

automatic variable management-- Shifts burden to the machine

-- “Glue” languages -- Acceptable execution speed

-- Lower level

-- Compiled-- More detail-oriented-- Manual variable management-- Pre-declared variables-- More programmer effort

-- “Coding” languages -- Optimize execution speed Rexx, Perl, Python,Tcl/Tk, Ruby, others C/C++, COBOL,

Java, Pascal, others

Scripting Traditional



When to Use Rexx

-- 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 speedis required

-- Systems -level programming

(No BIOS interrupts, directaddressing, etc.)

No Yes



Performance

Year-- 1981 1988 1993 1998 2005Mhz-- 4.77 8 66 266 3 ghzCPU-- 8088 386 486 PII PIV

704k

10k

200k

3M

Ratio of compiler to interpreter speed remains constant whileprocessor speeds increaseexponentially



II. Why Rexx ?



Why Rexx Vs Other Scripting Languages ?

“ Easy bu t Powerfu l ”

• 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 $$$

Ease of use benefits exper ienced developers ...

“Easy but Powerful”



Rexx uses specific technologiesto tie them together


Power Simplicity

Conf l ict !



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



Power Through Simplicity…

Rexx presents a radically differentphilosophy on how to achieve

power than the “Unix tradition”languages (Perl, Bash, Korn, Awk, etc.)

Rexx presents a unique

sc r ipt ing paradigm



The Language Structure Makes Rexx Easy

Operators Arithmetic

Comparison

Logical

String 2 dozen Instructions

70 Built-inFunctions

Other Features OS commands, external functions, DLLs, APIs, widgets, etc.

Learn fromthe inside out



Rexx Runs Everywhere… Linux-- all versionsUnix-- all versionsBSD-- all versionsWindows-- all versionsMac OS-- all versionsDOS all versions (32- and 16- bit), IBM PC-DOS 2000 and 7

Handhelds-- Windows CE / Mobile / PPC / etc, Palm OS,Symbian/EPOC32, EPOC, DOS emulation

Embedded-- Embedded Linux, DOS, Windows variants

Mainframes-- z/OS, z/VM, z/VSE (all versions)IBM iSeries-- i5/OS, OS/400 (all versions)

Many others-- AmigaOS, AROS, MorphOS, OpenVMS, BeOS,OpenEdition, AtheOS/Syllable, SkyOS,QNX (QNX4/QNX6), OS/2, eCS, osFree, more…

Rexx predominates on systems in red



Rexx Has Crit ical Mass ...

Open sou rce, general pu rpos e scr ipt ing languages wi th cri t ical mass --

* Run everywhere (on all major OS‟s and platforms) * Have strong standards* Enjoy wide use and offer good support

* Internationally* In many spoken languages

* Offer thousands of free tools and scripts* Interface to everything (databases, web programming, GUIs, etc, etc)

NOTE-- The chart excludes non-o en source e VB VBScri t and non- eneral ur ose e PHP scri tin lan ua es

Cri t ical mass

Do no t have cri t ical mass

Perl

Python

Rexx, Tcl/Tk, Ruby

Many other good languages

(Ko rn, C-shel l, bash, Bourne, Lua,

Mumps, etc)



The Free Rexx Interpreters

Windows, DOS (32/16 bit),Windows CE, Linux, Unix,Mac OS, AmigaOS, others

All major operating systems

Windows

Unix, Linux, BSD

Windows Palm OS

WindowsLinux, Windows,Solaris, AIX

Any JavaEnvironment

Regina Rexx/imc

Reginald

roo!

Rexx for Palm OS

r4

BRexx

NetRexx Open Object

Rexx OOP

extensions



Rexx Free Tools and Interfaces • Over 2000 free tools & scripts 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 . . .



III. Let’s Code !



/*******************************************************************/ /* 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) > 0 /* 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

Example Script # 1…



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 f i le def in i t ion • 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



What is “Power” ? 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 problemin a reliable, readable, maintainable manner



Example Script # 2…

arg filein fgrep PAYMENT_OVERDUE filein

This script does the same thing as Example #1



The Power of Glue Languages

• Rexx evaluates a statement, sends anythingthat is not Rexx to the “external environment” (by default this is the OS)

• Full power of a string-manipulation languageto direct external interfaces

• Inspect return code, command output, messages,and respond

• Rexx is a glue language

Structured Control Instructions



Structured Control Instructions Do End If If then else

Do While

(case) Call

Subroutineor Function

Select

Un Structured Control Instructions



Un-Structured Control Instructions Do Until

Do Forever

Iterate

Leave Signal

(goto)



Rexx Functions…

• 70 Built-in Functions:

• String manipulation (character, bit, hex)

• Word manipulation• I/O• Numeric• Environmental

• Conversion• Other

• 2 statements access external funct ion l ibrary

• Those functions are then coded just like built-ins

Example Script # 3



Example Script # 3… /*******************************************************************/ /* Code Lookup: */ /* Looks up the area code for the town the user enters. */ /*******************************************************************/ area. = '' /* Initialize array entries to null */ area.CHICAGO = 312 /* Define a table of area codes */area.HOMEWOOD = 708area.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 end



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(con tent-addressable memory or associat ive memo ry )

• 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

Example Script # 4



Example Script # 4… /* 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'

(part I)

Example Script # 4 ( t II)



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 end if count >= weight then /* Display titles matching the criteria */

say title.j end



Discussion

• Array keyword. is a looku p table or l is t • key/value pairs like Perl or Berkeley DB

• Array title. is a t ree

• Trees can be balanced or not

DO I = 1 TO n BY m WHILE condition FOR xDO UNTIL … DO FOREVERDO n

IF condition THEN DO. . .END

ELSE DO. . .

END

Enclose multiple statementswithin a DO END pair

DO

IF

Create Any Data Structure With Rexx Arrays :



Create Any Data Structure With Rexx Arrays : Element 1 Element 2 Element 3 A Simple List

or Look-up Table Key-value Pairs

Key 1 Value 1 Key 2 Value 2 Key 3 Value 3 Key 4 Value 4

Balanced Tree Un-Balanced Tree

b.1b.1.1b.1.2

b.2b.2.1b.2.2

b.3b.3.1

b.3.2

b.1b.1.1

b.2

b.2.1b.2.2b.2.3

b.3b.4

b.1b.1.1

b.1.1.1b.1.1.2

b.2b.2.1b.2.2

b.2.3b.3

b3.1b.3.1.1

b.3.1.1.1 A Multi-level Tree

(unbalanced) Also: linked list, doubly

linked list, stack, queue,dequeue, etc...



Example-- Creating a Linked Lis t list.0 = HEAD ; list.0.next = 1 /* Define linked list. */list.1 = 'a' ; list.1.next = 2 /* You could also */list.2 = 'b' ; list.2.next = 3 /* 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 = 2 /* Point new item to next */list.1.next = 99 /* Point to the new item */

call display_linked_list /* Display the linked list */exit

display_linked_list: /* Displays the linked list*/sub = 0do while list.sub.next <> TAIL

say 'Element:' list.subsub = list.sub.next

end return

Wh R V Oth



For a language that “lacks data structures,”

Rexx sure has a lot of them!

Power thru Simpl ic i ty !




IV. More abou t Rexx



Rexx Standards

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

Extensions



Rexx Standards

1990

Early

90s

TRL-2 SAA

1996

ANSI

4.00 5.00LanguageLevel

TRL-1

3.50

1985



The Evolution of Rexx

Standard or “Classic” Rexx

Object-oriented Rexx

NetRexx(for Java

environments)

Mid 1990s Early 1980s



Windows CE BRexxPalm OS Rexx for Palm OSSymbian / EPOC32 Regina

PocketDOSXTMothers BRexx

+ Faster

+ Integrates with native services

+ Integrates with...+ DOS Services+ DOS Applications

+ Many DOS appsinstantly availablewithout any changes

Native DOS Emulation

Rexx on Handhelds

Interpreter: Interpreter:



How DOS Emulation Works

PC Hardware Native operating system

Rexx Scripts Rexx Interpreter

DOS Operating System DOS Emulator

Each layer runs on topof the one

below it



Classic Rexx

Object-Oriented Rexx Means…

Classes and Methods PLUS

Inheritance & Derivation

Encapsulation

Abstraction

Polymorphism

Huge Class Library



ObjectRexx

Object Rexx Adds to Classic Rexx . . .

Complete ObjectOrientation

New Instructions

More Functions New Operators

Built-in Objects,Special Variables,many other features

Classes andMethods

And Much More



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 sides both



Classic Rexx

NetRexx Goes Beyond Classic Rexx…

Changed and Extended with . . .

New instructions

Data typing (“types”)

Indexed strings

Special names

Object orientation

Special methods

… and much more …

Java environment integration



Translate NetRexx sourceinto a Java program

Developing and Running NetRexx Scripts

Run

Source scriptEg: hello.nrx

To translate, compile and run in one step enter: nrc -run hel lo

Java fileEg: hello.java

Compile Java into bytecode

Class fileEg: hello.class

NetRexx interprets and/or compiles. Can generate commented,formatted Java code. Runs under JVM or stand-alone.



V. More Rexx Features

How Rexx



-- Built-in Functions

-- Functions you develop

-- Subroutines

-- Extensions and

Function Libraries

-- Operating System Commands

-- Commands to other environments

-- External Programs

-- API Interfaces to external features

-- API into Rexx

Supports Modularity InternalRoutines

Modularity

ExternalResources

String Processing Operations



g g p abc + abc abcabc Concatenation

Joins two or more strings abcabc

abc abc

Bifurcation

Splits a string

abcabc Parsing

Scans and analyzes a string, may split it intoits constituent components

abcdef Pattern Matching

Identifies patterns in strings

Parse Count = 2

Find “def”

P i O ti



Parsing Operations

Separate by wordsBy Words

abc abc abc

Separate , using , commas By Pattern

By NumericPattern

Columns: 1 5 9



The Two I/O Modes

linein lineout

lines

Character-oriented

Process one character at a time

charin charout chars

+ More portable + Reads “special” characters

Line-oriented

Process one line at a time



QUEUE

The Stack is both a Stack and a Queue PULL,

PARSE PULL PUSH

Rexx‟s Stack is a generalized communications mechanism

Rexx Supports Recursion



pp

CallScript X

End TestFufilled ?

Script X

Yes

No

HowRecursionWorks



Tip – Steps to Good Programming Style

Spacing & indentation Good variable names

Limit Nesting Comments

Structured Code Modularity

Error checking Ect !

Capitalization

D b i O ti



Debugging Options

SAY Instruction TRACE Instructionin 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

C diti / E ti T i



signal on condi t ion name label_name

Condition / Exception Trapping

label_name:

…code of the main routine...

…code of the error handling routine...

Conditions: error, failure, halt, novalue, notready, syntax, lostdigits



VI. Conclusions



Conclusions

• Free & open source languages have taken over

• Scripting is the “quiet revolution”

• Rexx offers “Power through Simplicity”

• Useful addition to your toolbox

Resources



Resources Find everyth ing at www.RexxInfo.org

-- download Rexx-- download tools

-- tutorials, articles, how-to‟s -- reference materials

Rexx Programmer’s Reference at Amazonwww.amazon.com/rexx

http://www.amazon.com/gp/product/images/0764579967/ref=dp_primary-product-display_0/104-6473230-7259947?%5Fencoding=UTF8&n=507846&s=books



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