This article contains instructions, advice, or how-to content .(September 2022) |
This article contains a list of miscellaneous information.(September 2022) |
Paradigm | multiparadigm: procedural, structured |
---|---|
Designed by | Mike Cowlishaw |
Developer | Mike Cowlishaw, IBM |
First appeared | 1979 |
Stable release | ANSI X3.274 / 1996 |
Typing discipline | Dynamic |
Filename extensions | .cmd, .bat, .exec, .rexx, .rex, EXEC |
Major implementations | |
VM/SP R3, [1] TSO/E V2, [2] SAAREXX, [3] [4] ARexx, BREXX, Regina, [5] Personal REXX, REXX/imc | |
Dialects | |
NetRexx, Object REXX, now ooREXX, KEXX | |
Influenced by | |
PL/I, ALGOL, EXEC, EXEC 2 | |
Influenced | |
NetRexx, Object REXX | |
|
Rexx (Restructured Extended Executor) is a high-level programming language developed at IBM by Mike Cowlishaw. [6] [7] Both proprietary and open source Rexx interpreters exist for a wide range of computing platforms, and compilers exist for IBM mainframe computers. [8] Rexx is used for scripting, application macros and application development. As a general purpose scripting language, Rexx is considered a precursor to Tcl and Python.
Rexx is supported in a variety of environments. It is the primary scripting language in some operating systems including OS/2, MVS, VM, AmigaOS and is used for macros in some software including SPF/PC, KEDIT, THE and ZOC. With an engine installed, Rexx can be used for scripting and macros in programs that use a Windows Scripting Host ActiveX scripting engine (such as VBScript or JScript). Rexx is supplied with VM/SP Release 3 on up, TSO/E Version 2 on up, OS/2 (1.3 and later, where it is officially named Procedures Language/2), AmigaOS Version 2 on up, PC DOS (7.0 or 2000), ArcaOS, [9] and Windows NT 4.0 (Resource Kit: Regina). In the late 1980s, Rexx became the common scripting language for IBM Systems Application Architecture, where it was renamed "SAA Procedure Language REXX".
A script is associated with a Rexx interpreter at runtime in various ways based on context. In mainframe computing, a Rexx script or command is sometimes referred to as an EXEC since that is the name of the file type used for similar CMS EXEC, [10] and EXEC 2 [11] scripts and for Rexx scripts on VM/SP R3 through z/VM. The first line of a script specifies the use of a Rexx interpreter in a comment either by identifying the code as Rexx language or by file path via EXTPROC
. On MVS, Rexx scripts may [a] be recognized by the low level qualifier "EXEC" or if the first line fetched from SYSPROC is a comment containing "REXX" then it is treated as Rexx (rather than CLIST), and a script fetched from SYSEXEC must be Rexx. On OS/2, Rexx scripts share the filename extension ".cmd" with other scripting languages, and the first line of the script specifies the interpreter to use. On Linux, Rexx scripts generally begin with a shebang. Rexx macros for Rexx-aware applications use extensions determined by the application.
Originally, the language was called REX, short for Reformed Executor, but an extra "X" was added to avoid confusion with other products. The name was originally all uppercase because that was the only way to represent it in mainframe code at the time. Both editions of Mike Cowlishaw's first book on the language use all-caps, REXX, although the cover graphic uses mixed case. His book on NetRexx uses mixed case but all caps in the cover graphic with large and small caps, NETREXX. An expansion that matches the abbreviation, REstructured eXtended eXecutor, was used for the system product in 1984. [12] The name Rexx (mixed case) is used in this article, and is commonly used elsewhere.
Objective and subjective attributes of Rexx include:
Some claim that Rexx is a relatively simple language. With only 23 instructions (such as call
, parse
, and select
), it has a relatively small instruction set. Rexx has limited punctuation and formatting requirements. Rexx has only one data type, the character string. Some claim that such simplicities make Rexx relatively easy to debug.
Some claim that Rexx code looks similar to PL/I code, but has fewer notations. With fewer notations, it tends to be is harder to parse via a translator, but is easier to write. Simplifying coding was intentional as noted by the Rexx design goal of the principle of least astonishment. [12]
On his own time, Mike Cowlishaw developed the language and an interpreter for it in assembly language between 20 March 1979 and mid-1982 with the intent to replace the languages EXEC and EXEC 2. [6] Mike also intended Rexx to be a simplified and easier to learn version of PL/I, but some claim that Rexx has problematic differences from PL/I.
Rexx was first described in public at the SHARE 56 conference in Houston, Texas, in 1981, [13] where customer reaction, championed by Ted Johnston of SLAC, led to it being shipped as an IBM product in 1982.
Over the years IBM included Rexx in almost all of its operating systems (VM/CMS, MVS TSO/E, IBM OS/400, VSE/ESA, AIX, PC DOS, and OS/2), and has made versions available for Novell NetWare, Windows, Java, and Linux.
The first non-IBM version was written for PC DOS by Charles Daney in 1984/5 [7] and marketed by the Mansfield Software Group (founded by Kevin J. Kearney in 1986). [6] The first Rexx compiler appeared in 1987, written for CMS by Lundin and Woodruff. [14] Other versions have also been developed for Atari, AmigaOS, Unix (many variants), Solaris, DEC, Windows, Windows CE, Pocket PC, DOS, Palm OS, QNX, OS/2, Linux, BeOS, EPOC32/Symbian, AtheOS, OpenVMS, [15] : p.305 Apple Macintosh, and Mac OS X. [16]
ARexx, a Rexx interpreter for Amiga, was included with AmigaOS 2 onwards and was popular for scripting and application control. Many Amiga applications have an "ARexx port" which allows control of the application via a Rexx script. Notably, a Rexx script can switch between Rexx ports to control multiple applications.
In 1990, Cathie Dager of SLAC organized the first independent Rexx symposium, which led to the forming of the Rexx Language Association. Symposia are held annually.
Several freeware versions of Rexx are available. In 1992, the two most widely used open-source ports appeared: Ian Collier's REXX/imc for Unix and Anders Christensen's Regina [5] (later adopted by Mark Hessling) for Windows and Unix. BREXX is well known for WinCE and Pocket PC platforms, and has been "back-ported" to VM/370 and MVS.
OS/2 has a visual development system from Watcom VX-REXX. Another dialect was VisPro REXX from Hockware.
Portable Rexx by Kilowatt and Personal Rexx by Quercus are two Rexx interpreters designed for DOS and can be run under Windows as well using a command prompt. Since the mid-1990s, two newer variants of Rexx have appeared:
In 1996 American National Standards Institute (ANSI) published a standard for Rexx: ANSI X3.274–1996 "Information Technology – Programming Language REXX". [17] More than two dozen books on Rexx have been published since 1985.
Rexx marked its 25th anniversary on 20 March 2004, which was celebrated at the Rexx Language Association's 15th International REXX Symposium in Böblingen, Germany, in May 2004.
On October 12, 2004, IBM announced their plan to release their Object REXX implementation's sources under the Common Public License. Recent releases of Object REXX contain an ActiveX Windows Scripting Host (WSH) scripting engine implementing this version of the Rexx language.
On February 22, 2005, the first public release of Open Object Rexx (ooRexx) was announced. This product contains a WSH scripting engine which allows for programming of the Windows operating system and applications with Rexx in the same fashion in which Visual Basic and JScript are implemented by the default WSH installation and Perl, Tcl, Python third-party scripting engines.
As of January 2017 [update] Rexx was listed in the TIOBE index as one of the fifty languages in its top 100 not belonging to the top 50. [18]
In 2019, the 30th Rexx Language Association Symposium marked the 40th anniversary of Rexx. The symposium was held in Hursley, England, where Rexx was first designed and implemented. [19]
RexxUtil– a package of file and directory functions, windowed I/O, and functions to access system services such as WAIT and POST – is available for most Rexx environments. [20] [21] [22]
Rexx/Tk– a toolkit for graphics to be used in Rexx programmes in the same fashion as Tcl/Tk – is widely available.
RxxxEd– an integrated development environment (IDE) for Rexx – was developed for Windows. [15] RxSock for network communication as well as other add-ons to and implementations of Regina Rexx have been developed, and a Rexx interpreter for the Windows command line is supplied in most resource kits for various versions of Windows and works in DOS as well.
This section contains instructions, advice, or how-to content .(December 2012) |
Rexx has three types of statement
addressfoo/* set default environment for bare expression */ bar/* equivalent to address foo bar */
The language provides loop control similar to many other languages. A loop begins with do
and ends with end
. In the related NetRexx, the keyword loop
is used instead of do
, and ooRexx treats loop
and do
the same.
A loop is aborted (early exit) via leave
and short-circuited (continued) via iterate
.
The language supports testing a condition either before (do while
) or after (do until
) executing a block of code via syntax:
do while [condition] [instructions] end
do until [condition] [instructions] end
A loop can increment a variable and stop when a limit is reached.
do index = start [tolimit] [byincrement] [forcount] [instructions] end
The increment value is 1 if the by
clause is omitted. The loop continues forever if the limit to
clause is omitted.
The language permits counted loops, where an expression is computed at the start of the loop and the instructions within the loop are executed that many times:
doexpression [instructions] end
The language supports an unconditional loop via forever
that continues until the loop is aborted or the program is terminated.
do forever [instructions] end
Like PL/I, Rexx allows both conditional and repetitive elements to be combined in the same loop: [23]
do index = start [tolimit] [by increment] [forcount] [whilecondition] [instructions] end
do expression [untilcondition] [instructions] end
The language provides for conditional execution via if
, then
and else
for a block delimited by do
and end
.
if [condition] thendo [instructions] endelsedo [instructions] end
For a single instruction block, do
and end
can be omitted.
if [condition] then [instruction] else [instruction]
The language provides multiple condition branching via select
which derives from the SELECT;
form of the PL/I SELECT
statement [b] . Like similar constructs in other dynamic languages, Rexx's when
clauses specify full conditions – not equality tests of a single value for the statement as some languages do. In that, they are more like cascading if-then-else
code than like the C or Java switch
statement.
selectwhen [condition] then [instruction or nop] when [condition] thendo [instructions or nop] endotherwise [instructions or nop] end
The nop
instruction is required if no action is associatd with a when
condition.
The otherwise
clause is optional. If omitted and no when
conditions are met, then the syntax
condition is raised.
Variables are typeless and initially are evaluated as their names in upper case. Thus a variable's type can vary with its use in the program:
sayhello/* => HELLO */ hello=25sayhello/* => 25 */ hello="say 5 + 3"sayhello/* => say 5 + 3 */interprethello/* => 8 */drophello sayhello/* => HELLO */
If no novalue
condition handler is configured, then an undefined variable evaluates to its name, in upper case. The built-in function SYMBOL
returns "VAR" for a defined variable and does not trigger novalue
even if not defined. The VALUE
function gets the value of a variable without triggering a novalue
condition, but its main purpose is to read and set environment variables, similar to POSIX getenv
and putenv
.
The language provides the compound variable construct which supports adding fields (called tails) to a variable (called a stem in this context) to support data structures such as lists, arrays, n-dimensional arrays, sparse or dense arrays, balanced or unbalanced trees and records.
The language does not provide special support for numeric array indexing like many other languages do. Instead, a compound variable with numeric tails produce a similar effect. [24]
The following code defines variables stem.1 = 9, stem.2 = 8, stem.3 = 7
...
doi=1to10stem.i=10-i end
Unlike a typical array, a tail (index) need not identify (be named) an integer value. For example, the following code is valid:
i='Monday' stem.i=2
A default value can be assigned to a stem via .
but no tail.
stem.='Unknown' stem.1='USA' stem.44='UK' stem.33='France'
In this case stem.3
, for example, evaluates to the default value, 'Unknown'
.
The whole stem (including any default value) can be erased with the drop
statement.
dropstem.
By convention (not part of the language) the compound stem.0
is often used to keep track of how many items are in a stem, for example a procedure to add a word to a list might be coded like this:
add_word:procedureexposedictionary.parseargw n=dictionary.0+1dictionary.n=w dictionary.0=n return
A stem can have multiple tails. For example:
m='July' d=15 y=2005 day.y.m.d='Friday'
Multiple numerical tail elements can be used to provide the effect of a multi-dimensional array.
Features similar the compound variable are found in other languages including associative arrays in AWK, hashes in Perl and Hashtables in Java, dynamic objects in Javascript. Most of these languages provide an mechanism to iterate over the keys (tails) of such a construct, but this is lacking in classic Rexx. Instead, it is necessary to store additional information. For example, the following procedure might be used to count each occurrence of a word.
add_word:procedureexposecount.word_list parseargw.count.w=count.w+1/* assume count. has been set to 0 */ifcount.w=1thenword_list=word_listw return
and then later:
doi=1towords(word_list)w=word(word_list,i)saywcount.w end
More recent Rexx variants, including Object REXX and ooRexx, provide a construct to iterate over the tails of a stem.
doioverstem.sayi'-->'stem.i end
The parse
instruction provides string-handling via syntax:
parse [upper] origin [template]
If upper
is included then the input is converted to upper case before parsing.
origin describes the input as one of the following:
arg
– arguments, at top level tail of command linelinein
– standard input, e.g. keyboardpull
– Rexx data queue or standard inputsource
– info on how program was executedvalue
expressionwith
–with
indicates the end of the expressionvar
– a variableversion
– version/release numbertemplate can be a combination of variables, literal delimiters, and column number delimiters.
Using a list of variables as template:
myVar="John Smith"parsevarmyVarfirstNamelastName say"First name is:"firstName say"Last name is:"lastName
displays:
First name is: JohnLast name is: Smith
Using column number delimiters:
myVar="(202) 123-1234"parsevarMyVar2AreaCode57SubNumber say"Area code is:"AreaCode say"Subscriber number is:"SubNumber
displays:
Area code is: 202Subscriber number is: 123-1234
The interpret
instruction evaluates its argument as a Rexx statement allowing for evaluation of code formatted at runtime. Uses include passing a function as a parameter, arbitrary precision arithmetic, use of the parse
statement with programmatic templates, stemmed arrays, and sparse arrays.[ how? ] The following example displays 16 and exits.
X='square'interpret'say'X||'(4) ; exit'SQUARE:returnarg(1)**2
The Valour software package relied upon Rexx's interpretive ability to implement an OOP environment.[ citation needed ] Another use was found in an unreleased Westinghouse product called Time Machine that was able to fully recover following an otherwise fatal error.[ citation needed ]
saydigits()fuzz()form()/* => 9 0 SCIENTIFIC */say999999999+1/* => 1.000000000E+9 */numericdigits10/* only limited by available memory */say999999999+1/* => 1000000000 */say0.9999999999=1/* => 0 (false) */numericfuzz3say0.99999999=1/* => 1 (true) */say0.99999999==1/* => 0 (false) */say100*123456789/* => 1.23456789E+10 */numericformengineering say100*123456789/* => 12.34567890E+9 */say53//7/* => 4 (rest of division)*/
numericdigits50 n=2 r=1doforever/* Newton's method */rr=(n/r+r)/2ifr=rrthenleaver=rr endsay"sqrt"n' = 'r
sqrt 2 = 1.414213562373095048801688724209698078569671875377
numericdigits50 e=2.5 f=0.5don=3f=f/n ee=e+f ife=eethenleavee=ee endsay"e ="e
e = 2.7182818284590452353602874713526624977572470936998
The signal
instruction configures the runtime to run custom code to handle a system condition if triggered. Conditions include:
error
– Positive return code from a system commandfailure
– Negative return code from a system command (e.g. command doesn't exist)halt
– Abnormal terminationnovalue
– A variable name was used but the variable is not definednotready
– Input or output error (e.g. read attempts beyond end of file)syntax
– Invalid program syntax, or some other error conditionlostdigits
– Significant digits were lost (ANSI Rexx, not in TRL second edition)The following fragment prints a message when the user terminates (halts) it:
signalonhalt;doa=1saya do100000/* a delay */endendhalt:say"The program was stopped by the user"exit
Since Rexx version 4, a handler can be named. In the following example, the handler ChangeCodePage.Trap
is configured to handle a syntax
condition.
ChangeCodePage:proceduresignalonsyntaxnameChangeCodePage.Trap returnSysQueryProcessCodePage() ChangeCodePage.Trap:return1004
When a condition is handled (as configured via signal on
), the condition can be analyzed via RC
which indicates the last error code and SIGL
which indicates the line number of the code that triggered the condition.
BASIC is a family of general-purpose, high-level programming languages designed for ease of use. The original version was created by John G. Kemeny and Thomas E. Kurtz at Dartmouth College in 1963. They wanted to enable students in non-scientific fields to use computers. At the time, nearly all computers required writing custom software, which only scientists and mathematicians tended to learn.
In computer programming, a macro is a rule or pattern that specifies how a certain input should be mapped to a replacement output. Applying a macro to an input is known as macro expansion.
A shell script is a computer program designed to be run by a Unix shell, a command-line interpreter. The various dialects of shell scripts are considered to be command languages. Typical operations performed by shell scripts include file manipulation, program execution, and printing text. A script which sets up the environment, runs the program, and does any necessary cleanup or logging, is called a wrapper.
Bytecode is a form of instruction set designed for efficient execution by a software interpreter. Unlike human-readable source code, bytecodes are compact numeric codes, constants, and references that encode the result of compiler parsing and performing semantic analysis of things like type, scope, and nesting depths of program objects.
The mIRC scripting language is the scripting language embedded in mIRC and Adiirc, IRC clients for Windows but work with WiNE for Linux.
Job Control Language (JCL) is a scripting language used on IBM mainframe operating systems to instruct the system on how to run a batch job or start a subsystem. The purpose of JCL is to say which programs to run, using which files or devices for input or output, and at times to also indicate under what conditions to skip a step. Parameters in the JCL can also provide accounting information for tracking the resources used by a job as well as which machine the job should run on.
In some programming languages, eval
, short for evaluate, is a function which evaluates a string as though it were an expression in the language, and returns a result; in others, it executes multiple lines of code as though they had been included instead of the line including the eval
. The input to eval
is not necessarily a string; it may be structured representation of code, such as an abstract syntax tree, or of special type such as code
. The analog for a statement is exec, which executes a string as if it were a statement; in some languages, such as Python, both are present, while in other languages only one of either eval
or exec
is.
TI-BASIC is the official name of a BASIC-like language built into Texas Instruments' graphing calculators. TI-BASIC is a language family of three different and incompatible versions, released on different products:
XEDIT is a visual editor for VM/CMS using block mode IBM 3270 terminals.
A source-code editor is a text editor program designed specifically for editing source code of computer programs. It may be a standalone application or it may be built into an integrated development environment (IDE).
Object REXX is a high-level, general-purpose, interpreted, object-oriented (class-based) programming language. Today it is generally referred to as ooRexx, which is the maintained and direct open-source successor to Object REXX.
ARexx is a Rexx interpreter for Amiga, written in 1987 by William S. Hawes, with a number of Amiga-specific features beyond standard Rexx. An ARexx script can communicate with software that implements an ARexx port. An Amiga application can define a set of commands and functions for ARexx to address, thus making the capabilities of the software available to an ARexx script. Several applications support running an ARexx script as a macro.
CMS EXEC, or EXEC, is an interpreted, command procedure control, computer scripting language used by the CMS EXEC Processor supplied with the IBM Virtual Machine/Conversational Monitor System (VM/CMS) operating system.
EXEC 2 is an interpreted, command procedure control, computer scripting language used by the EXEC 2 Processor originally supplied with the CMS component of the IBM Virtual Machine/System Product (VM/SP) operating system.
NetRexx is an open source, originally IBM's, variant of the REXX programming language to run on the Java virtual machine. It supports a classic REXX syntax, with no reserved keywords, along with considerable additions to support object-oriented programming in a manner compatible with Java's object model, yet can be used as both a compiled and an interpreted language, with an option of using only data types native to the JVM or the NetRexx runtime package. The latter offers the standard Rexx data type that combines string processing with unlimited precision decimal arithmetic.
A batch file is a script file in DOS, OS/2 and Microsoft Windows. It consists of a series of commands to be executed by the command-line interpreter, stored in a plain text file. A batch file may contain any command the interpreter accepts interactively and use constructs that enable conditional branching and looping within the batch file, such as IF
, FOR
, and GOTO
labels. The term "batch" is from batch processing, meaning "non-interactive execution", though a batch file might not process a batch of multiple data.
LOLCODE is an esoteric programming language inspired by lolspeak, the language expressed in examples of the lolcat Internet meme. The language was created in 2007 by Adam Lindsay, a researcher at the Computing Department of Lancaster University.
The syntax and semantics of PHP, a programming language, form a set of rules that define how a PHP program can be written and interpreted.
LEXX is a text editor which was probably the first to use live parsing and colour syntax highlighting for marked-up text and programs. It was written by Mike Cowlishaw of IBM in 1985. The name was chosen because he wrote it as a tool for lexicographers, during an assignment for Oxford University Press's 'New Oxford English Dictionary'. The program ran on mainframes under VM/CMS. LEXX's design was based on several other editors written by the same author augmented by the ability to dynamically parse text and display colour on the new colour terminals that had recently become available. It is programmable using dynamically-loaded compiled commands or using interpreted commands.
In computing, a script is a relatively short and simple set of instructions that typically automate an otherwise manual process. The act of writing a script is called scripting. A scripting language or script language is a programming language that is used for scripting.
Could there be a high astonishment factor associated with the new feature? If a feature is accidentally misapplied by the user and causes what appears to him to be an unpredictable result, that feature has a high astonishment factor and is therefore undesirable. If a necessary feature has a high astonishment factor, it may be necessary to redesign the feature.