REXX

• character string orientation

• dynamic data typing (no declarations)

• automatic storage management

• crash protection

• content-addressable data structures

• straight-forward access to system commands and facilities

• a rich selection of built-in functions

• simple error-handling and built-in debugger

• few artificial limitations

REXX looks a lot like PL/1.

Table of contents

1 History 2 Syntax 2.1 Looping 2.2 Conditionals 2.3 Testing for multiple conditions 2.4 PARSE 3 Under /A> 3.5 Spelling

History

Originally a scripting language developed at IBM. REXX was the successor to the script languages EXEC and EXEC 2. It was also designed to be a macro or scripting language for any system. As such, it is a precursor to TCL and Python.

Over the years IBM developed versions for many of its operating systems: VM/CMS, /A>, PC-DOS, MVS/TSO, AS/400, and AIX. Non-IBM versions have also been developed for Atari, Unix, DEC, Windows, and MS-DOS. Later versions of the Amiga OS included a version of REXX called AREXX.

Several freeware versions are available. REXX/IMC and Regina are the most widely-used open-source ports to Windows and Linux.

In 1996 ANSI published a standard for REXX: ANSI X3.274-1996 "Information Technology - Programming Language REXX"

In recent years, two newer variants of REXX have appeared:

• NetRexx - which compiles to java byte-code.
• ObjectRexx - which is an object-oriented variant of REXX.

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 /H2>

REXX is included in the base operating system of OS/2, a REXX program begins with matched comment delineaters, /* */, to indicate to the OS that it is a REXX program:

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

Instructions between quotes are passed to the OS:

   /* sample.cmd */
   'di/w'
   

Spelling

Cowlishaw seems to prefer Rexx, whereas IBM sales, ANSI, and the majority of the web uses 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.