Tips and Tricks from Another Source
REXX Tips & Tricks - Version 1.8 27
I'm sure if you are either a professional programmer using REXX or a casual REXX user
you have a place where you store miscellaneous bits of information that you save for future
reference. You then have to remember where that tiny fragment that you read about some
particular REXX command or function is salted away.
Bernd Schemmer of Frankfurt, Germany has made life simpler for all of us by
collecting these REXX-related tidbits and publishing them collectively. If there's been a
helpful suggestion or tip posted in any of the electronic forums devoted to REXX, its a good
bet that it is included in Schemmer's collection. He updates this free file on a regular basis
and amazes this REXX professional with the breadth of the material he has gathered into a
single document. His report is available on many electronic repositories with a file name of
rxtt18.exe (with the numeric portion of the file name indicating the release level of the file).
The self-extracting file expands into an .inf file that can be viewed and searched with the
OS/2 VIEW program like any of the system .inf files.
Since Schemmer's first language is German, you may find an occasional incorrect
word usage or grammatical structure that is not quite correct but the hundreds of items
contained in his Tips & Tricks is otherwise well presented. He credits all of his sources and
provides hyper-linked references to the appropriate source's E-mail addresses. Some of the
subject matter is not explained in enough detail to provide a full explanation of the topic;
however, the mere presence of the topic is frequently enough to provide insight into the
matter being discussed. Table 1 contains a brief list of the hundreds topics contained in Tips
& Tricks.
Tips & Tricks contains numerous
sample programs that can be extracted
from the .inf file. Schemmer details a
technique to extract these program using
the View program menu entries Services /
Copy to File while the window with the
source code is the active window. The View
program creates a file named text.tmp in the
current directory. You can then adjust the
contents of text.tmp for your own needs and
save it as a .cmd file.
While I'm pleased to say that I have
contributed numerous items to this
extensive collection of REXX-related items,
I always manage to find something that
makes me say "I didn't know that" each time
Schemmer releases an updated version of
his Tips & Tricks. With Schemmer's
permission, I have included some of the
more obscure items. I have made some
minor corrections to spelling and grammar.
Special environment variables for
REXX programs
The following environment variables have
a special meaning for REXX programs:
RXTRACE - If the environment variable
RXTRACE is set to ON before executing a
REXX program, the REXX program is
executed in single step mode. This is the equivalent of including the REXX TRACE command
with the parameter ?R. Any other value for the RXTRACE variable is ignored by the REXX
interpreter. To prevent the execution of a REXX program in single step mode even if the
environment variable RXTRACE is set to ON, use the statement: CALL TRACE 'OFF' as first
statement of your program. This is very useful to prevent tracing programs like PMREXX or
a REXX program "compiled" with programs like REXXCC.
RXQUEUE - This environment variable contains the name of the queue which the program
RXQUEUE.EXE (subcommand) should use if the queue name is NOT specified within
RXQUEUE is launched. The default queue name used by RXQUEUE is the default REXX data
queue name of SESSION.
Output & Input control
To ensure that the output of your program goes to the screen regardless of the current target
for STDOUT use:
call LineOut "CON", "This output always goes to the screen!"
rather than outputting the line with the SAY instruction. To print messages to STDOUT or
STDERR you can use these names for the output device. For example:
/* print a string to STDERR */
call LineOut "STDERR",,
"This output goes to STDERR"
/* print a string to STDOUT */
call LineOut "STDOUT", "This output goes to STDOUT"
To ensure that the input for your program comes from the keyboard regardless of the current
source for STDIN use
userInput = LineIn( "CON" )
It is important to note that functions LINEOUT and LINEIN use normal file handles for the
output devices. Therefore, be sure to close the device with the STREAM function after using
it. Note that there is no way to direct output to the handles 3 to 9 in REXX.
Special variables
A special variable is one that may be set automatically during processing of a REXX program.
There are 3 special variables used by the classic REXX interpreter and 5 special variables in
Object Oriented REXX.
RC - This special variable contains the return code of the last external non-REXX
command called; for example, OS/2 commands like DIR or EAUTIL. In case of a SYNTAX error
this variable is set to the syntax error number (1-99). After an ERROR or FAILURE condition
RC contains the command return code. Commands executed manually while tracing
interactively do not change the value of RC.
RESULT - This special variable contains the return code of an internal or external
REXX function if called with the CALL statement. The special variable RESULT is dropped if
the REXX function doesn't return a return code. RESULT is also dropped if the function is
called in an implicit or explicit assignment (a = myFunc(); if myFunc() = 4 then).
SELF (Object Oriented REXX only) - This special variable is set when a method is
activated. Its value is the object that forms the execution context for the method (that is, the
receiver object of the activating message).
SIGL - This special variable is set to the line number of the last instruction that caused
a transfer of control to a label (any SIGNAL, CALL, internal function call, or trapped
condition).
SUPER (Object Oriented REXX only) - This special variable is set when a method is
activated. Its value is the class object that is the usual starting point for a super class method
lookup for the SELF object.
All of these special variables can be changed just like any other REXX variable. You
should save the values of the special variables in another variable if you want to use them
in other statements.
Opening files
The default mode for opening files in REXX is READ/WRITE (even if you open the file
implicitly via the LINEIN() function). This prevents other programs from opening the file even
if the first program opening this file only wants to read from the file. To avoid this, I
(Schemmer) suggest you use an explicit call to the STREAM() function to open a file in READ
mode if you only want to read from it.
Closing files
Because the number of possible file handles is restricted in OS/2 sessions, you should always
close every file you've opened as soon as possible. You also need to close a file (and perhaps
reopen it again) if you want to call another program to write into or read from this file. You
should only use
call STREAM filename , "C", "CLOSE"
to close a file. The other method, using LINEOUT or CHAROUT without the second parameter,
is only valid for files to which you have write access (even if you've only read from the file).
Tips & Tricks contains the most complete list of OS/2 REXX-related freeware and
shareware that I have ever seen. Schemmer has also included the pertinent information
about all of the printed REXX books and articles currently available. Tip & Tricks almost has
too much information in it. However, since it is in .inf format and viewable with the standard
OS/2 VIEW program, you can search it by keyword for items of special interest to you.
Schemmer includes instructs for converting the .inf file to ASCII text or HTML format for
printing.
Object REXX
As I write this column, I have come to the conclusion that Object REXX may have
been left dangling in the breeze by IBM PSP. In addition, the person who has served as
the lead developer of Object REXX for the past couple of years has moved on and is
entrenched in his new surroundings at Lotus - not the IBM Glendale Laboratories in
Endicott, NY. However, I have been told that the new REXXUTIL API that I wrote about in
my August, 1995 column will still be released with the next version of Warp (code name
Merlin) - when and if that occurs.
Object REXX users who have been waiting for a newer beta than that which was
made available on the DevCon 8 CD-ROM will have to wait for DevCon 10. The IBM
Developer Connection folks in Boca Raton have announced that
the DevCon 9 CD-ROM will not contain any updates to Object REXX.
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