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REXX

Table of contents

1 Features 2 History 3 Syntax 3.1 Looping 3.2 Conditionals 3.3 Testing for multiple conditions 3.4 PARSE 4 Under OS/2 5 Spelling 6 External links

Features

• character string basis
• dynamic data typing (no declarations)
• no reserved keywords (except in local context)
• decimal arithmetic (floating-point)
• a rich selection of built-in functions (especially string and word processing)
• automatic storage management
• crash protection
• content-addressable data structures
• straightforward access to system commands and facilities
• simple error-handling, and built-in tracing and debugger
• few artificial limitations
• simplified I/O facilities.

REXX syntax looks similar to PL/I, but has fewer notations; this makes it harder to parse (by program) but easier to use.

History

It was first described in public at the SHARE 56 conference in Houston, Texas, in 1981, where customer reaction, championed by Ted Johnston of SLAC, led to it being shipped as an IBM product in 1982.

Over the years IBM included REXX in almost all of its operating systems (VM/CMS, VM/GCS, MVS TSO/E, AS/400, OS/2, VSE/ESA, AIX, CICS/ESA, and PC-DOS), and has made versions available for Novell Netware, Windows, Java, and Linux.

The first non-IBM version was written for PC-DOS by Charles Daney in 1984/5. Other versions have also been developed for Atari, Amiga, Unix (many variants), Solaris, DEC, Windows, WinCE, PocketPC, MS-DOS, Palm OS, QNX, OS/2, Linux, BeOS, EPOC32, AtheOS, OpenVMS, OpenEdition, Macintosh, and MacOS X.

Several freeware versions are available. REXX/imc and Regina are the most widely-used open-source ports to Windows and Linux. BREXX is well-known for WinCE and PocketPC platforms.

In 1996 ANSI published a standard for REXX: ANSI X3.274-1996 “Information Technology – Programming Language REXX”. More than two dozen books on REXX have been published since 1985.

In the last decade, two newer variants of REXX have appeared:

• NetRexx - which compiles to Java byte-code via Java source code; this has no reserved keywords at all, and uses the Java object model, and is therefore not upwards-compatible with ‘classic’ REXX
• ObjectRexx - which is an object-oriented upwards-compatible version of REXX.

Rexx marked its 25^th anniversary on 20 March 2004, which was celebrated at the REXX Language Association]’s 15^th International REXX Symposium in Böblingen, Germany, in May 2004.

Syntax

Looping

The DO control structure always begins with a DO and ends with an END.

DO UNTIL:

   do until [condition]
   [instructions]
   end

DO WHILE:

   do while [condition is true]
   [instructions]
   end

   do i = x to y by z
   [instructions]
   end

   do forever
     if [condition] then leave
   end

   do i = x to y by z for a
   [instructions]
   end

Conditionals

Testing conditions with IF

   if [condition] then
     do
     [instructions]
     end
   else
     do
     [instructions]
     end

For single instructions, DO and END can also be omitted:

   if [condition] then
     [instruction]
   else
     [instruction]

Testing for multiple conditions

SELECT is REXX’s CASE structure

   select
     when [condition] then
     do
     [instruction]
     end
   otherwise
     do
     [instruction] or NOP
     end

NOP indicates no instruction is to be executed.

PARSE

The PARSE instruction is particularly powerful; it combines some useful string-handling functions. Its syntax is:

   parse [upper] origin template

where origin specifies the source:

• arg (command line variable)
• linein (keyboard)
• pull (REXX data queue)
• source (OS/2 info on how program was executed)
• value (a literal or a function)
  • the keyword with required to indicate where the literal ends
• var (a variable)
• version (version/release number)

   myVar = "John Smith"
   parse var MyVar firstName lastName
   say "First name is:" firstName
   say "Last name is:"  lastName

   First name is: John
   Last name is: Smith

   myVar = "Smith, John"
   parse var MyVar LastName "," FirstName
   say "First name is:" firstName
   say "Last name is:"  lastName

   First name is: John
   Last name is: Smith

   myVar = "(202) 123-1234"
   parse var MyVar 2 AreaCode 5  7 SubNumber
   say "Area code is:" AreaCode
   say "Subscriber number is:" SubNumber

   Area code is: 202
   Subscriber number is: 123-1234

Under OS/2

REXX is included in the base operating system of OS/2, and is also used as the macro language in many applications. Under OS/2, a REXX program begins with matched comment delimiters, /* */, to indicate to the operating system that it is a REXX program:

   /* sample.cmd */
   say "Hello World"

Instructions between quotes are passed to the OS:

   /* sample.cmd */
   'dir /p /w'

Spelling

In plain text, Cowlishaw seems to prefer Rexx, whereas IBM documents and the majority of the web uses REXX. The ANSI standard uses the form preferred by the standardization committee, which has small capitals for the final three letters: REXX.

External links

• REXX language page at IBM
• REXX Language Association
• Quercus Systems: Commercial REXX interpreter for Windows, OS/2, and DOS.
• Regina: open-source REXX interpreter for Linux, BSD, Windows, etc.