Redirected from Rexx programming language
REXX has just twenty-three, largely self-evident keywords (ie, CALL, PARSE, SELECT) and minimial 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[?].
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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:
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
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]
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.
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:
and template can be:
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.
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'
Cowlishaw seems to prefer Rexx, whereas IBM sales, ANSI, and the majority of the web uses REXX.
wikipedia.org dumped 2003-03-17 with terodump