ARexx
Encyclopedia
ARexx is an implementation of the REXX
language for the Amiga
, written in 1987 by William S. Hawes, with a number of Amiga-specific features beyond standard REXX facilities. Like most REXX implementations, ARexx is an interpreted language
. Programs written for ARexx are called "scripts", or "macros"; several programs offer the ability to run ARexx scripts in their main interface as macros.
ARexx can easily communicate with third-party software that implements an "ARexx port". Any Amiga application or script can define a set of commands and functions for ARexx to address, thus making the capabilities of the software available to the scripts written in ARexx.
ARexx can direct commands and functions to several applications from the same script, thus offering the opportunity to mix and match functions from the different programs. For example, an ARexx script could extract data from a database
, insert the data into a spreadsheet
to perform calculations on it, then insert tables and charts based on the results into a word processor
document.
in the book The REXX Language: A Practical Approach to Programming. ARexx was included by Commodore
into AmigaOS
2.0 in 1990. This later version of ARexx follows the official REXX language closely; Hawes was later involved in drafting the ANSI
standard for REXX.
ARexx is written in 68000 Assembly, and cannot therefore function at full speed with new PPC CPUs, a version of ARexx has not been rewritten for them and is still missing in MorphOS
2.0. William Hawes is no longer involved in development of Amiga programs because of quarrels in the past with Commodore about the licensing of ARexx, and no other Amiga-related firm is financing new versions of ARexx. Notwithstanding this fact, the existing version of ARexx continues to be used, although it is not distributed with MorphOS.
From the ARexx manual:
ARexx can increase the power of a computer by combining the capabilities of various programs. Because of the popularity of a stand-alone ARexx package, Commodore included it with Release 2 of AmigaDOS
.
Like all REXX implementations, ARexx uses typeless data representation. Other programming languages made distinctions between integers, floating point numbers, strings, characters, vectors, etc. In contrast, REXX systems treat all data as strings of characters, making it simpler to write expressions and algorithms.
As is often the case in dynamically-scoped languages, variables are not declared before using them, they come into being on their first use.
ARexx scripts benefit from an error handling system which monitors execution and responds accordingly. The programmer can choose to suspend and resume the execution of the program as needed.
The ARexx command set is simple, but in addition to the commands there are the functions of its Amiga reference library (rexxsyslib.library). It is also easy to add other libraries or individual functions. ARexx scripts can also be invoked as functions from other ARexx scripts. Any Amiga program which has an ARexx port built in can share its functions with ARexx scripts.
The following script is a very minimal ARexx script that displays warnings depending on events that take place.
/* Alarm.rexx */
ARG event
IF event = 0 THEN EXIT
IF event = 1 THEN SAY "Program has ended unexpectedly"
IF event = 2 THEN SAY "Program has finished its job"
IF event = 3 THEN SAY "Cannot find data in selected directory"
REXX
REXX is an interpreted programming language that was developed at IBM. It is a structured high-level programming language that was designed to be both easy to learn and easy to read...
language for the Amiga
Amiga
The Amiga is a family of personal computers that was sold by Commodore in the 1980s and 1990s. The first model was launched in 1985 as a high-end home computer and became popular for its graphical, audio and multi-tasking abilities...
, written in 1987 by William S. Hawes, with a number of Amiga-specific features beyond standard REXX facilities. Like most REXX implementations, ARexx is an interpreted language
Interpreted language
Interpreted language is a programming language in which programs are 'indirectly' executed by an interpreter program. This can be contrasted with a compiled language which is converted into machine code and then 'directly' executed by the host CPU...
. Programs written for ARexx are called "scripts", or "macros"; several programs offer the ability to run ARexx scripts in their main interface as macros.
ARexx can easily communicate with third-party software that implements an "ARexx port". Any Amiga application or script can define a set of commands and functions for ARexx to address, thus making the capabilities of the software available to the scripts written in ARexx.
ARexx can direct commands and functions to several applications from the same script, thus offering the opportunity to mix and match functions from the different programs. For example, an ARexx script could extract data from a database
Database
A database is an organized collection of data for one or more purposes, usually in digital form. The data are typically organized to model relevant aspects of reality , in a way that supports processes requiring this information...
, insert the data into a spreadsheet
Spreadsheet
A spreadsheet is a computer application that simulates a paper accounting worksheet. It displays multiple cells usually in a two-dimensional matrix or grid consisting of rows and columns. Each cell contains alphanumeric text, numeric values or formulas...
to perform calculations on it, then insert tables and charts based on the results into a word processor
Word processor
A word processor is a computer application used for the production of any sort of printable material....
document.
History
ARexx was first created in 1987, developed for the Amiga by William S. Hawes. It is based on the REXX language described by Mike CowlishawMike Cowlishaw
Mike Cowlishaw is a retired IBM Fellow, a Visiting Professor at the Department of Computer Science at the University of Warwick, and is a Fellow of the Royal Academy of Engineering , the Institute of Engineering and Technology , and the British Computer Society.- Career at IBM :Cowlishaw joined IBM...
in the book The REXX Language: A Practical Approach to Programming. ARexx was included by Commodore
Commodore International
Commodore is the commonly used name for Commodore Business Machines , the U.S.-based home computer manufacturer and electronics manufacturer headquartered in West Chester, Pennsylvania, which also housed Commodore's corporate parent company, Commodore International Limited...
into AmigaOS
AmigaOS
AmigaOS is the default native operating system of the Amiga personal computer. It was developed first by Commodore International, and initially introduced in 1985 with the Amiga 1000...
2.0 in 1990. This later version of ARexx follows the official REXX language closely; Hawes was later involved in drafting the ANSI
Ansi
Ansi is a village in Kaarma Parish, Saare County, on the island of Saaremaa, Estonia....
standard for REXX.
ARexx is written in 68000 Assembly, and cannot therefore function at full speed with new PPC CPUs, a version of ARexx has not been rewritten for them and is still missing in MorphOS
MorphOS
MorphOS is an Amiga-compatible computer operating system. It is a mixed proprietary and open source OS produced for the Pegasos PowerPC processor based computer, PowerUP accelerator equipped Amiga computers, and a series of Freescale development boards that use the Genesi firmware, including the...
2.0. William Hawes is no longer involved in development of Amiga programs because of quarrels in the past with Commodore about the licensing of ARexx, and no other Amiga-related firm is financing new versions of ARexx. Notwithstanding this fact, the existing version of ARexx continues to be used, although it is not distributed with MorphOS.
From the ARexx manual:
"ARexx was developed on an Amiga 1000 computer with 512k bytes of
memory and two floppy disk drives. The language prototype was
developed in C using Lattice C, and the production version was written
in assembly-language using the Metacomco assembler. The documentation
was created using the TxEd editor, and was set in using Amiga.
This is a 100% Amiga product."
Characteristics
ARexx is a programming language that can communicate with other applications. Using ARexx, for example, one could request data from a database application and send it to a spreadsheet application. To support this facility, an application must be "ARexx compatible" by being able to receive commands from ARexx and execute them. A database program might have commands to search for, retrieve, and save data — the MicroFiche Filer database has an extensive ARexx command set. A text editor might have ARexx commands corresponding to its editing command set — the Textra editor supplied with JForth can be used to provide an integrated programming environment. The AmigaVision multimedia presentation program also has ARexx port built in and can control other programs using ARexx.ARexx can increase the power of a computer by combining the capabilities of various programs. Because of the popularity of a stand-alone ARexx package, Commodore included it with Release 2 of AmigaDOS
AmigaDOS
AmigaDOS is the disk operating system of the AmigaOS, which includes file systems, file and directory manipulation, the command-line interface, and file redirection....
.
Like all REXX implementations, ARexx uses typeless data representation. Other programming languages made distinctions between integers, floating point numbers, strings, characters, vectors, etc. In contrast, REXX systems treat all data as strings of characters, making it simpler to write expressions and algorithms.
As is often the case in dynamically-scoped languages, variables are not declared before using them, they come into being on their first use.
ARexx scripts benefit from an error handling system which monitors execution and responds accordingly. The programmer can choose to suspend and resume the execution of the program as needed.
The ARexx command set is simple, but in addition to the commands there are the functions of its Amiga reference library (rexxsyslib.library). It is also easy to add other libraries or individual functions. ARexx scripts can also be invoked as functions from other ARexx scripts. Any Amiga program which has an ARexx port built in can share its functions with ARexx scripts.
Implementing new features and capabilities via scripts
If end user is using a program which builds animations by joining various bitmap image files but which lacks image processing capabilities, he could write an ARexx script which performs these actions:- ARexx locates the image files in their directories
- ARexx loads first image
- ARexx loads paint program
- The image is loaded into paint program which performs modifications to file
- The modified image is stored into another directory
- ARexx repeats procedure on any image in the directory
- The paint program is closed and the animation program is loaded
- The animation is built
- The animation is saved in its directory
- The animation program is closed
Avoiding repetitive procedures
EqFiles.rexx is a well known example of a simple ARexx script written to automate repetitive and boring procedures. This script uses the ALeXcompare program to compares files, and then finds all duplicates in a set of files and returns output by highlighting any results in a different color.Expand AmigaOS capabilities
One of the main features of ARexx is the fact it could expand the capabilities of the AmigaOS by adding some procedures the OS lacked. For example a simple ARexx program could be written to print a warning message on the screen of the monitor, or play an audio alert signal if a certain Amiga program stops, faults or has finished its scheduled job.The following script is a very minimal ARexx script that displays warnings depending on events that take place.
/* Alarm.rexx */
ARG event
IF event = 0 THEN EXIT
IF event = 1 THEN SAY "Program has ended unexpectedly"
IF event = 2 THEN SAY "Program has finished its job"
IF event = 3 THEN SAY "Cannot find data in selected directory"
External links
- Beginning ARexx Tutorial
- [ftp://ftp.aminet.net/docs/help/arexxreference.lha Command and Function Reference]
- Design Tool