ARexx can easily communicate with third-party software that implements an "ARexx port". Any Amiga application 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.
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 or post-Commdore releases of AmigaOS.
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.
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:
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.
One of the main features of ARexx is the fact it could expand the capabilities of an OS (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 on the monitor screen depending on events that take place.
/* Alarm.rexx */
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"