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Frequently Asked Questions About REXX
Last Revised: August 12, 1994
Eric Giguere
giguere@watcom.on.ca
----------------------------------------------------------------
Copyright Information
This document is Copyright 1993, 1994 by Eric Gigu<67>re.
Permission is granted to reproduce and distribute all or
part of this document for non-commercial purposes only. All
other uses must first be cleared with the author. The
author may be contacted on the Internet at the address
giguere@watcom.on.ca or on paper by writing to Watcom
International, 415 Phillip Street, Waterloo, Ontario,
Canada, N2L 3X2. Please note, however, that this document
is not published or endorsed by Watcom.
----------------------------------------------------------------
Introduction
This document is intended to serve as a useful reference for
REXX-related information. It aims for breadth as opposed to
depth, and references to other material are given where
appropriate. Suggestions and updates should be sent to the
author in an attempt to keep this document relevant and up-
to-date.
Readers will notice the prevalence of OS/2-related materials
in this document. Most of the REXX-related activity at this
time is occurring on the OS/2 platform. This document is
not intended to be OS/2-specific. The author is quite happy
to include information on other platforms if you pass it on
to him.
More information on REXX can also be had from the REXX Language
Association. See below for details.
----------------------------------------------------------------
A. What Is REXX?
REXX is a programming language designed by Michael Cowlishaw
of IBM UK Laboratories. In his own words: "REXX is a
procedural language that allows programs and algorithms to
be written in a clear and structured way."
REXX doesn't look that different from any other procedural
language. Here's a simple REXX program:
/* Count some numbers */
say "Counting..."
do i = 1 to 10
say "Number" i
end
What makes REXX different from most other languages is that
it is also designed to be used as a macro language by
arbitrary application programs. The idea is that
application developers don't have to design their own macro
languages and interpreters. Instead they use REXX as the
macro language and support the REXX programming interface.
If a REXX macro comes across an expression or function call
that it cannot resolve, it can ask the application to handle
it instead. The application only has to support the
features that are specific to it, freeing the developer from
handling the mundane (and time-consuming) task of writing a
language interpreter. And if all applications use REXX as
their macro language, the user only has to learn one
language instead of a dozen.
----------------------------------------------------------------
B. REXX and the Internet
Networks connect computers in various ways for the exchange
of data. The terminology is a bit confusing to the new
user. Here are the definitions this document uses:
Usenet: Not really a network, just the set of machines
that exchange network news. Network news is really an
extended form of electronic mail that groups messages
from individuals into newsgroups that users can read
using special newsreaders.
Internet: The worldwide network based on TCP/IP
protocols. Besides being able to receive mail and
newsgroups, these machines can use programs like ftp and
telnet to communicate with other machines in real time.
Most Internet machines are Unix-based.
BITNET: The worldwide network that connects many IBM
mainframes. BITNET users can also transfer files using
methods that are incompatible with those of the Internet.
Newsgroups
The Usenet group comp.lang.rexx exists for discussion of
REXX in all its variations. Anything posted to this
newsgroup also gets sent to the REXXLIST mailing list (see
below) and vice-versa.
Other newsgroups of interest are machine-specific.
Recommended groups are comp.os.os2.programmer.misc and
comp.sys.amiga.programmer.
FTP Sites of Interest
FTP is a file transmission protocol used on the Internet to
transfer files between machines. The transfers are done in
real time and usually require that the user have an account
on both machines. However, many machines on the Internet
support what is known as anonymous FTP, which allows users
on other machines access to a limited set of files without
requiring an account. Some of the more interesting sites
that offer this service are:
rexx.uwaterloo.ca General repository for REXX-related
information, including free REXX
interpreters for Unix and DOS. An
XEDIT clone for Unix and OS/2 may
also be found here. Look under
/pub/rexx.
ftp.pvv.unit.no The official home of Regina, one of
the free Unix interpreters. Archives
of the messages in comp.lang.rexx and
RexxLA messages are also maintained
here. Check under /pub/rexx.
ftp-os2.cdrom.com General OS/2 archives. Look under
ftp.luth.se /pub/os2.
wuarchive.wustl.edu General Amiga archive. Look under
/pub/aminet.
Mailing Lists
Mailing lists are similar to newsgroups but use normal
electronic mail to deliver the messages. The following
mailing lists are mostly BITNET-based but are accessible
from the Internet as well:
List name BITNET Internet Discusses
Node Address
REXXLIST UCF1VM ucf1vm.cc.ucf.edu REXX in general
AREXX-L UCF1VM ucf1vm.cc.ucf.edu Amiga REXX
PC-REXX UCF1VM ucf1vm.cc.ucf.edu Personal REXX
REXXCOMP UCF1VM ucf1vm.cc.ucf.edu IBM's REXX compiler
TSO-REXX UCF1VM ucf1vm.cc.ucf.edu TSO REXX
VM-REXX UCF1VM ucf1vm.cc.ucf.edu VM/SP REXX
UREXX-L (none) liverpool.ac.ak Unix REXX
To subscribe to any of these lists, send a one-line message
to the address LISTSERV@node, where node is the BITNET node
or Internet address for the list you wish to join. In the
body of your message should be the line
SUBSCRIBE list-name your--full-name
as in
SUBSCRIBE UREXX-L Eric Giguere
You will then be subscribed to the list and messages will
start arriving in your mailbox. To send a message to the
list, simply mail it to listname@node, as in UREXX-
L@liverpool.ac.uk. Note the distinction between the
LISTSERV address and the listname address. You can receive
help by sending a HELP message to the LISTSERV address.
Note that some of these mailing lists may be available on
Usenet in the form of newsgroups with names starting with
"bit.listserv". Ask your system administrator if you're not
sure.
Thanks to Scott Ophof for providing this summary.
Gopher Service
Gopher clients may find REXX-related information at the site
gopher.pvv.unit.no (Europe) and index.almaden.ibm.com (N. America).
----------------------------------------------------------------
C. Free REXX Products
Interpreters
There are at least three REXX interpreters available for
free on the Internet. The first two are Unix based and are
well-supported by their authors. The third is an MS-DOS
interpreter.
Regina is Anders Christensen's REXX interpreter for various
flavours of Unix and VMS. It is fairly complete and Anders
even has an API for developers. It also apparently can be
ported to OS/2. Anders can be reached at
anders@pvv.unit.no. Regina's official home is
ftp.pvv.unit.no.
REXX/imc is Ian Collier's REXX interpreter for SunOS, though
it has also been ported to other Unix systems. Ian can be
reached at imc@prg.ox.ac.uk.
BREXX is Bill Vlachoudis' REXX interpreter for MS-DOS. The
interpreter is not complete but is quite small. Bill can be
reached at bill@donoussa.physics.auth.gr.
All three interpreters are available for anonymous FTP on
rexx.uwaterloo.ca in the /pub/freerexx directory, each
interpreter in its own subdirectory. Regina and REXX/imc
are in source form, BREXX is only available as binary.
REXX-Aware Text Editors
Also on rexx.uwaterloo.ca in the /pub/editors directory is
the text editor THE by Mark Hessling
(mark@snark.itc.gu.edu.au). THE is a full-featured
XEDIT/KEDIT clone (by XEDIT here we mean the IBM mainframe
text editor, not the X Windows editor xedit) with REXX
support. THE is available in versions for OS/2 and Unix.
THE's official home is on ftp.gu.edu.au in /src/THE.
----------------------------------------------------------------
D. Commercial REXX Products
Interpreters
REXX interpreters are available commercially for a wide
variety of systems and come standard on some operating
platforms such as the Amiga, OS/2 and the IBM AS/400 and
mainframes (VM, TSO, VSE). The following vendors sell
REXX interpreters:
The Workstation Group [Various UNIX platforms, also VMS]
6300 River Road
Rosemont, IL 60018
(800) 228-0255 (US only)
sales@wrkgrp.com
Quercus Systems [DOS, Windows, Windows NT, OS/2]
P.O. Box 2157
Saratoga, CA 95070
(408) 867-7399
(800) 440-5944 (US & Canada)
75300.2450@compuserve.com
Simware [Novell Netware]
2 Gurdwara Road
Ottawa, Ontario
Canada K2E 1A2
(613) 727-1779
IBM also sells REXX interpreters for AIX and Netware.
Compilers
Although REXX is usually thought of as an interpreted
language, it can also be compiled. The following vendors
all sell REXX compilers:
Dineen Edwards Group [Amiga]
19785 West 12 Mile Road, Suite 305
Southfield, MI 48076-2553
(313) 352-4288
IBM [VSE, MVS/TSO and VM/CMS]
Contact your local representative
Systems Center [VM/CMS]
1800 Alexander Bell Drive
Reston, VA 22091
Visual Development Environments
There are three REXX-based visual development environments
available for OS/2:
VX-REXX Watcom International
415 Phillip Street
Waterloo, Ontario
Canada N2L 3X2
Phone: (519) 886-3700
Fax: (519) 747-4971
VisPro/REXX HockWare
315 N. Academy St., Suite 100
Cary, NC 27513
Phone: (919) 380-0616
Fax: (919) 380-0757
GpfRexx Gpf Systems
10 Falls Road
Moodus, Conn. 06469
Phone: (203) 873-3300
Fax: (203) 873-3302
REXX-Aware Text Editors
Clones of the popular XEDIT editor are available for Unix
from the Workstation Group (see address above) and for DOS
and OS/2 from Mansfield Software. Tritus sells an ISPF/PDF
text editor with REXX support for OS/2. One Up sells SourceLink,
an integrated development environment for OS/2 with REXX macro
capabilities. Command Technology sells the SPF/PC editor.
Mansfield Software
P.O. Box 532
Storrs, CT 06268
Phone: (203) 429-8402
Fax: (203) 487-1185
Tritus
3300 Bee Caves Road, Suite 650
Austin, Texas 78746
Phone: (512) 794-5800
Fax: (512) 7940-3833
One Up
1603 LBJ Freeway, Suite 200
Dallas, Texas 75243
Phone: (800) 678-0187
Command Technology
1040 Marina Village Parkway
Alameda, CA 94501
Phone: (800) 336-3320
The OS/2 Enhanced Editor (EPM.EXE), which is bundled with
OS/2, also has REXX support. Use its online help and search
for the 'rx' command.
REXX Extensions
A number of vendors sell extensions to REXX:
-- Quercus Systems (address above) sells REXXLIB (a collection
of over 150 REXX extension functions), REXXCOMM (a function
package for accessing serial ports from REXX) and REXXTERM
(a full-featured asynchronous communications program).
-- SofTouch Systems sells the GammaTech REXX SuperSet/2, a
collection of over 300 REXX extension functions for OS/2.
-- dSoft Development sells the dbfREXX function library that
lets you read and write dBASE files from OS/2 REXX.
SofTouch Systems
1300 S. Meridian, Suite 600
Oklahoma City, Okla. 73108-1751
Phone: (405) 947-8080
Fax: (405) 632-6537
dSoft Development
4710 Innsbruk Drive
Houston, Texas 77066
Phone: (405) 360-3045
Fax: (713) 537-0318
----------------------------------------------------------------
E. REXX and ANSI
The American National Standards Institute (ANSI) sets
national standards for various things in the United States,
including programming languages. The X3J18 REXX Standards
Committee is currently defining a formal standard for the
REXX language, using Mike Cowlishaw's book as its base
document. The Committee meets 3 or 4 times a year and holds
ongoing discussions throughout the year by electronic mail.
Members of X3J18 are mostly REXX implementors, but anyone
can participate. The Committee intends to release a draft
standard next year. More information can be had from the
vice-chair, Neil Milsted at nfnm@wrkgrp.com.
Note that public ANSI documents relating to X3J18 can be had
using the LISTSERV service at PSUVM on BITNET or by Gopher
to gopher.pvv.unit.no on the Internet.
----------------------------------------------------------------
F. The REXX Language Association
The REXX Language Association is an independent organization
dedicated to promoting the use of the REXX programming
language. Activities of the RexxLA include:
-- Maintaining an electronic mail server where members share
information.
-- Distributing a quarterly newsletter.
-- Providing electronic resources for access to language
expertise, hints and tips, example programs, product sources,
and other valuable information.
-- Developing resource guides, both printed and electronic,
for publications, products, training and language experts.
-- Developing educational, guest speaker, and publicity programs
to promote the use of REXX.
-- Participating in the work of standards bodies.
-- Promoting integration of REXX into all operating systems and as
the common scripting language for a wide array of software.
-- Cooperating with the REXX Symposium in providing an annual
conference forum.
Join today and start reaping the benefits available from an
international consortium of individuals, corporations, vendors,
authors and experts.
For more information, contact the REXX Language Association by
mail or fax:
RexxLA Membership
6300 North River Road, Suite 501
Rosemont, Illinois 60018
Fax: (708) 696-2277
Or by electronic mail at rexxla@wrkgrp.com.
----------------------------------------------------------------
G. The REXX Symposium
The REXX Symposium is an annual conference devoted to REXX,
attended both by users and vendors, held at the beginning
of May. It is sponsored by the Stanford Linear Accelerator,
with the cooperation of the RexxLA. The 1995 conference
is still being planned.
----------------------------------------------------------------
H. REXX Bibliography
Mike Cowlishaw and Linda Green have kindly provided the
following partial bibliography of REXX books.
The REXX Language -- M.F. Cowlishaw
English: ISBN 0-13-780735-X Prentice-Hall, 1985
ISBN 0-13-780651-5 2nd edition, 1990
German: ISBN 3-446-15195-8 Carl Hanser Verlag, 1988
ISBN 0-13-780784-8 P-H International, 1988
Japanese: ISBN 4-7649-0136-6 Kindai-kagaku-sha, 1988
The REXX Reference Summary Handbook -- Dick Goran
ISBN 0-9639854-1-8, CFS Nevada Inc., 1994
Modern Programming Using REXX -- Robert P. O'Hara and
David R. Gomberg
English: ISBN 0-13-597311-2 Prentice-Hall, 1985
ISBN 0-13-579329-5 2nd edition, 1988
REXX in the TSO Environment -- Gabriel F. Gargiulo
ISBN 0-89435-354-3, QED Information Systems Inc.
320 pages, 1990
Using OS/2 REXX -- Gabriel F. Gargiulo
ISBN 0-894-35449-3, QED Publishing Group
Practical Usage of REXX -- Anthony S. Rudd
ISBN 0-13-682790-X, Ellis Horwood (Simon & Schuster), 1990
Using ARexx on the Amiga -- Chris Zamara and Nick Sullivan
ISBN 1-55755-114-6, Abacus Books, 1991
The REXX Handbook -- Edited by Gabe Goldberg and Phil Smith III
ISBN 0-07-023682-8, McGraw-Hill, 1991
Programming in REXX -- Charles Daney
ISBN 0-07-015305-1, McGraw-Hill, 1992
Command Language Cookbook -- Hallett German
ISBN 0-442-00801-5, Van Nostrand Reinhold, 1992
OS/2 2.1 REXX Handbook -- Hallett German
ISBN 0-442-01734-0, Van Nostrand Reinhold, 1994
OS/2 REXX: From Bark to Byte -- Inter. Technical Supp. Org. (IBM)
IBM Document Number GG24-4199-00, 1993
REXX: Advanced Techniques for Programmers -- Peter Kiesel
ISBN 0-07-034600-3, McGraw Hill, 1992
REXX Tools and Techniques -- Barry Nirmal
ISBN 0-89435-417-5, QED Publishing Group, 1993
The ARexx Cookbook -- Merrill Callaway
ISBN 0-96-327730-8, Whitestone, 1992
Writing OS/2 REXX Programs -- Ronny Richardson
ISBN 0-07-052372, McGraw Hill, 1992
Writing VX-REXX Programs -- Ronny Richardson
ISBN 0-07-9111911-5, McGraw Hill, 1994
=====================================================================
I. Common REXX Coding Errors
The following list of common REXX coding errors is derived from a list
included in the online documentation for Watcom VX-REXX.
-----------------------------------------------------------------
1. Blank space where it does not belong
In REXX expressions, blank space is interpreted as an implicit
concatenation operator -- the terms are concatenated with a blank
in between. As a result, REXX will interpret many mistyped statements
as an expression involving the blank concatenation operator.
For example, inserting a blank after a function name in a function call
changes the meaning of the expression from:
text_upper = translate( text )
to:
text_upper = "TRANSLATE" || " " || text
Blank space also plays a special role in the PARSE instruction. Compare
the following:
parse arg a b c
parse arg a, b, c
The first line parses the first argument passed to the routine into three
parts, while the second line sets the three variables to the value of
the first three arguments passed to the routine.
-----------------------------------------------------------------
2. Function calls versus the CALL statement
When you call a routine that returns a result, you must enclose the
parameters in parentheses:
text = VRGet( "EF_1", "Value" )
Always assign the value of a function to a variable, or use
the CALL statement as described below.
Otherwise REXX will pass the return value to the default
host environment, leading to strange and possibly damaging behaviour
on some systems.
If you are calling a routine that does not return a value, or you
wish to ignore the return value, you should use the CALL instruction:
call VRSet "EF_1", "BackColor", "Blue"
Note that there is no comma between the name of the routine and the
first parameter. Note also that parentheses are not used when using
the CALL instruction.
-----------------------------------------------------------------
3. Line continuation
The comma is used in REXX to split clauses across two or more lines.
For example:
call foo a, b, c
can also be written as:
call foo a, ,
b, ,
c
It's easy to forget the second comma when breaking a line in the
middle of a function parameter list.
-----------------------------------------------------------------
4. Omitted arguments
REXX allows arguments to be omitted. Be careful not to omit
arguments by accident, such as including an unnecessary comma:
call foo , a, b, c
-----------------------------------------------------------------
5. Undefined variables
It is not a syntax error to use undefined variables in REXX.
Undefined variables are defined to have their own name translated
to uppercase as their value. As a result it is often difficult to
find programming errors that are a result of using undefined variables.
Some tips:
* Add a SIGNAL ON NOVALUE statement to the main section of your
programs. This will cause the system to issue a syntax error
if you use an undefined variable.
* Be careful to include the period when referring to stems.
The variables "A" and "A." are unrelated.
* Misspelled commands will often be interpreted as undefined variables.
The line:
sy 'hello'
(which should be "say 'hello'") will be interpreted as:
"SY" || " " || 'hello'
and will be send to the default command host for execution.
-----------------------------------------------------------------
6. Using expressions in the tail of a compound symbol
The tail of a compound symbol can only be a simple variable, as in:
ok = A.I
Literals are not allowed. For example, the following is interpreted as a concatenation between "A." and
"name":
bad = A."name"
Expressions are also not allowed. You must first assign the value of the expression to a symbol and then
use that symbol:
J = I - 1
ok = A.J
=====================================================================
G. Frequently Asked Questions
-----------------------------------------------------------
1. Is REXX better than <some other language>?
Short answer: Yes. No. Maybe. Does it matter?
Long answer: This question wastes a lot of bandwidth in
comp.lang.rexx and other newsgroups. Every language has its
good points and its bad points. Some people love REXX, some
people hate it. Use a language that suits your needs.
-----------------------------------------------------------
2. Why does my OS/2 REXX program run more quickly the second time?
When you run a REXX CMD file for the first time, a tokenized
version will be stored on disk using the OS/2 extended file
attributes. (You can see how big the tokenized version is
by using the /N option on the DIR command.) If a tokenized
version exists AND the file has not been modified, CMD.EXE
will use the tokenized version instead of parsing the
source.
Note that there is a 64K limit on the size of an extended
attribute entry, so very large REXX programs do not benefit
from this automatic tokenization.
-----------------------------------------------------------
3. How can I return multiple values from a function?
REXX does not provide any support for returning more than a
single value from a function. If you wish to return multiple values
, you must devise an alternate scheme. A simple solution is to
concatenate the values together into a single string and on return
from the function use the PARSE instruction or the various string
functions to split the string back into its elements. Don't forget
that you can use non-printable characters (such as '00'x) to
separate the data -- REXX will correctly handle such strings.
There may also be other alternatives available to you if you are
using an external function library that lets you store data in
separate memory pools or in disk files.
-----------------------------------------------------------
4. Why does linein, lineout, charin or charout fail?
Most versions of REXX (ARexx is an exception) use implicit file
opening. That is, each time you reference a file in a LINEIN,
LINEOUT, CHARIN or CHAROUT function, REXX will open the file for
reading or writing if the file is not already open. However, some
operating systems like DOS and OS/2 impose limits on the number of
files that can be open simultaneously, usually around 20 or so. After
the limit has been reached, any further attempts to open another file
will fail. That is why it is always good practice to close a file
when you're done with it. In OS/2 this is done using the STREAM
function, as follows:
call stream "c:\foo.out", "command", "close"
The STREAM function can also be used to open files, query their sizes
and seek into the file. Consult your REXX documentation for
specific instructions for your interpreter.
-----------------------------------------------------------
5. How do I iterate over all the tails in a stem variable?
One of the features REXX lacks is a function to return a list of
defined tails. There are external libraries that provide functions
to do so, but if that is not an option then the only solution is to
maintain your own list of tails in a string and use the PARSE
instruction or the WORDS function to traverse the list.
-----------------------------------------------------------
6. How do I REXX-enable my application?
REXX-enabling an application means being able to run REXX macros
within an application. This information is very system-specific,
so the best place to start is with the documentation provided with the
REXX interpreter.
For OS/2, there are several sources of information. The most basic
information is found in the OS/2 Toolkit, which includes the
REXXSAA.H header file and the REXX Reference online document. The
REXX Report (see above) includes a couple of articles on the subject.
Sample source code comes with the OS/2 Toolkit and is also available
on rexx.uwaterloo.ca in the directory /pub/os2/vxrexx as VX-REXX
Tech Notes #1 and #7 (vxtech01.zip, vxtech07.zip -- neither tech
note requires that you own VX-REXX). OS/2 technical conferences such
as ColoradOS/2 or the IBM Technical Interchanges often includes
sessions on this topic. For ARexx, a book was available from
Commodore, but with the latter's demise it is unclear whether the
book is still available.
-----------------------------------------------------------
7. How do I do inter-process communication in REXX?
Again, this is system-specific. The ARexx interpreter is built on
a messaging model, making it very simple to do inter-process
communication, but the OS/2 REXX interpreter has no such features,
though in some cases queues can be used to achieve the desired effect.
-----------------------------------------------------------
8. How do I use global variables in my REXX programs?
The scope of variables is controlled by the PROCEDURE instruction.
If a routine is declared with the PROCEDURE instruction, only
those variables exposed using the EXPOSE instruction are available to the
routine. If no PROCEDURE instruction is used, all of the caller's
variables are available to the callee. Here is a simple example:
a = 10
b = 20
call first
call second
call third
exit
first:
say "first -- a is" a "b is" b
return
second: procedure
say "second -- a is" a "b is" b
return
third: procedure expose a
say "third -- a is" a "b is" b
b = 30
call first
return
Running this program yields the following output:
first -- a is 10 b is 20
second -- a is A b is B
third -- a is 10 b is B
first -- a is 10 b is 30
Use the PROCEDURE instruction to keep variables local to a procedure,
using EXPOSE to explicitly expose any "global" variables. The
only catch is that you have to make sure you expose the variables
inside every procedure. One way to define and use global variables
is to use a stem called "Globals." and define all your procedures
like this:
Foo: procedure expose Globals.
Then at the top of you program initialize the Globals stem and
assign appropriate values to your global variables:
Globals. = ''
Globals.!NeedToSave = 0
Globals.!TmpDir = "D:\TMP"
The tail names in this example are all prefixed with '!', though you
could also use an underscore ('_'). This is just a convention
used to avoid this kind of problem:
Globals.TmpDir = "D:\TMP"
call Foo
say Globals.TmpDir
exit
Foo: procedure expose Globals.
tmpdir = "foo"
Globals.TmpDir = tmpdir
return
It's a subtle bug that has to do with how REXX interprets stem tails.