REXX

Features

• 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 has just twenty-three, largely self-evident keywords (ie, CALL, PARSE, SELECT) and minimal punctuation requirements. It is essentially a free-form language with only one data-type, the character string; users never have to worry about data conversion.

REXX looks a lot like PL/1.

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, OS/2, 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.

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

Stepping through a variable:

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

Looping forever until exiting with LEAVE:

do forever if [condition] then leave end

Looping a fixed number of times

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)

and template can be:

• list of variables
• column number delimiters
• literal delimiters

upper is optional; it you specify it, data will be converted to upper case.

Examples:

Using a list of variables as template

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

displays the following

First name is: John Last name is: Smith

Using a delimiter as template:

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

also displays the following

First name is: John Last name is: Smith

Using column number delimiters:

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

displays the following

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

A template can use a combination of variables, literal delimiters, and column number delimiters.

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 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 */ 'dir /p /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.

Referenced By