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Free Rexx ! Everything You Ever Wanted to Know

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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 Instructions
If 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 = '' then say 'Town' town 'is not in my database' else say 'The area code for' town 'is' 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 ; = /* Define linked list. */ list.1 = 'a' ; = /* You could also */ list.2 = 'b' ; = /* create it */ list.3 = TAIL ; = TAIL /* dynamically */ call display_linked_list /* Display the linked list */ list.99 = 'after a, before b' /* Add new item in list */ = /* Point new item to next */ = /* Point to the new item */ exit display_linked_list: /* Displays the linked list*/ sub = 0 do while <> TAIL say 'Element:' list.sub sub = 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: 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... ? ? ? ?

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