/* Main program */ 
st = .student~new 
st~StudentID = 1 
st~StudentName = ''Joe'' 
st~Marks1 = 10 
st~Marks2 = 20 
st~Marks3 = 30 
say st~Total(st~Marks1,st~Marks2,st~Marks3)  

exit 0 
::class Person 
::class student subclass Person 
::attribute StudentID 
::attribute StudentName 
::attribute Marks1 
::attribute Marks2 
::attribute Marks3 
::method ''Total'' 
use arg a,b,c 
return (ABS(a) + ABS(b) + ABS(c)) 

The output of the above program will be as shown below.

60

Rexx – Portability

Portability is an important aspect in any programming language. As one knows, Rexx is available in a variety of operating systems such as Windows and Linux. So it need to be ensured that when one develops a program on the Windows platform, that it has the necessary precautions taken if the same programs runs on a Linux platform.

Rexx has the ability to run system level commands. There are commands which can be used to understand what is the operating system on which it is running on. Based on the output it can then take the appropriate actions to see what are the commands that can be run on this operating system.

Example

The following example shows how the parse functions are used to get the details of the operating system on which the program is running.

/* Main program */ 
parse version language level date month year. 
parse source system invocation filename. 
language = translate(language) 

if pos(''REGINA'',language) = 0 then 
   say ''Error , the default interpreter is not Regina'' language 
   say ''The Interpreter version/release date is:'' date month year 
   say ''The Language level is: '' level say ''The Operating System is''  

   select 
when system = ''WIN32'' then 
   ''ver''
when system = ''UNIX'' | system = ''LINUX'' then 
   ''uname -a'' 
   otherwise 
   say ''Unknown System:'' system 
end 
if rc <> 0 then 
   say ''Error :'' rc 

The output will vary depending on operating system. A sample output is given below.

The Interpreter version/release date: 5 Apr 2015 
The Language level is:  5.00 
The Operating System is 
Unknown System: WIN64 
Bad return code: RC 

Rexx – Extended Functions

Rexx provides a number of extended functions that gives a wide variety of functionality, most of them which allow you to interact with the Operating System. Let’s look at some of them in detail as explained below.

Rexx – Instructions

Rexx provides a number of instructions that gives a wide variety of functionality, most of them which allow you to interact with the Operating System. Let’s look at some of them in detail.

Rexx – Implementations

The Rexx language has a lot of various implementations as we have already seen in the previous chapters. Each implementation has its own functionality. Let’s look at the various implementations available for Rexx.

OoRexx

This is the object oriented version of Rexx. By default, the Rexx basic implementation is all based on procedures. But with ooRexx you can offer greater flexibility by having an Object oriented approach to Rexx. By using ooRexx you can have better re-use through creating re-usable classes and objects.

The following program is an example of a simple Rexx program which can be run with the ooRexx implementer.

Example

/* Main program */ 
say ‘hello’ 

To run this program, run the following command.

rexx main.rexx 

When you run the above command, you will get the following output.

hello

Netrexx

This is for all Java based developers as it provides a Java based alternative for the Rexx language. So all of the objects are based on the Java Object Model. The advantage of this framework is that since Java is a widely popular language it becomes easier for developers to use this framework. So in this implementation, the Rexx code is converted to a Java program which can then be run on any Java virtual machine.

The following code is an example of a NetRexx program.

Create a file called main.nrx and place the following code in the file.

/* Main program */ 
say ‘hello’

To compile the code run the following command −

NetRexxC main.nrx 

You will then get the following output. NetRexxC is the compiler which converts the Rexx program to its java equivalent.

java -cp ";;G:NetRexx-3.04GAlibNetRexxF.jar;." 
-Dnrx.compiler = ecj org.netrexx.process.NetRexxC  main.nrx 
NetRexx portable processor 3.04 GA build 4-20150630-1657 
Copyright (c) RexxLA, 2011,2015.   All rights reserved. 
Parts Copyright (c) IBM Corporation, 1995,2008. 
Program main.nrx 
Compilation of ''main.nrx'' successful

You can now run your java program using the following java command.

java main 

When you run the above command, you will get the following output.

Hello

Brexx

This is a lightweight implementation of Rexx. This is a lighter package than the standard Rexx implementer. But it still has the full functionality of Rexx.

The following code is an example of a BRexx program.

/* Main program */ 
say ‘hello’

To run the program, run the following command.

rexx32 main.rexx

When you run the above command, you will get the following output.

hello

Rexx – Netrexx

NetRexx is the java implementation of Rexx. In NetRexx, the implementer is used to convert the Rexx program to a java program which can then be run on any Java virtual machine.

Setting up NetRexx

The first step in NetRexx is to set it up on the local machine. To do this, one needs to perform the following steps −

Step 1 − Go to the NetRexx download site − http://www.netrexx.org/downloads.nsp

Download the NetRexx.3.04.GA file.

Step 2 − Ensure that java is installed and running on your system. You can verify that java is running by using the java–version command.

An example of the output is shown below.

H:>java -version 
java version "1.7.0_79" 
Java(TM) SE Runtime Environment (build 1.7.0_79-b15) 
Java HotSpot(TM) Client VM (build 24.79-b02, mixed mode, sharing) 

Step 3 − Unzip the contents of the Netrexx zipped file. Copy the files from the NetRexx3.04GAlib folder to your java installation/lib/etc folder.

Step 4 − Add the NetRexx-3.04GAbin path to the path variable on the system.

Running the First NetRexx Program

Create a file called main.nrx and place the following code in the file.

/* Main program */ 
say ‘hello’ 

To compile the code run the following command.

NetRexxC main.nrx 

You will then get the following output. NetRexxC is the compiler which converts the rexx program to its java equivalent.

java -cp ";;G:NetRexx-3.04GAlibNetRexxF.jar;." 
-Dnrx.compiler = ecj org.netrexx.process.NetRexxC  main.nrx 
NetRexx portable processor 3.04 GA build 4-20150630-1657 
Copyright (c) RexxLA, 2011,2015.   All rights reserved. 
Parts Copyright (c) IBM Corporation, 1995,2008. 
Program main.nrx 
Compilation of ''main.nrx'' successful

You can now run your java program using the following java command.

java main 

When you run the above command, you will get the following output.

Hello

Let us now discuss some of the special aspects of the Netrexx library.

Indexed Strings

In NetRexx, strings can become the indexes to arrays. An example is shown below.

Example

/* Main program */ 
value = ''unknown'' 
value[''a''] = ''b'' 
c = ''a'' 
say value[c] 

When we run the above program, we will get the following result.

Output

b

Multiple Indexes

In NetRexx, you can have multiple indexes for arrays. An example is shown below.

Example

/* Main program */ 
value = ''null'' 
value[''a'', ''b''] = 1 
say value[''a'', ''b'']

When we run the above program we will get the following result.

Output

1

Rexx – Brexx

BRexx is a lighter weight implementation of Rexx. It still has a lot of functionality to offer as part of the Rexx implementation.

Setting up BRexx

The first step in BRexx is to set it up on the local machine. To do this, one needs to perform the following steps −

Step 1 − Go to the BRexx download site − https://ftp.gwdg.de/pub/languages/rexx/brexx/html/rx.html

Go to the downloads section and download the product.

Step 2 − Unzip the contents of the Brexx zipped file.

Step 3 − Add the BRexxbin path to the path variable on the system.

Step 4 − Create a new variable called RXLIB and point it to the lib folder in the Brexx folder.

Running the First BRexx Program

Create a file called main.rexx and place the following code in the file.

/* Main program */ 
say ‘hello’ 

To run the program, run the following command.

rexx32 main.rexx 

When you run the above command, you will get the following output.

hello

Let us now discuss some of the most commonly used functions available in the BRexx library.

Rexx – Databases

Rexx has the ability to work with a variety of databases which are listed below.

• HSQLDB
• Oracle
• SQL Server
• MySQL
• MongoDB

All the information for Rexx databases can be found once you click on the following link − https://rexxsql.sourceforge.net/

In our example, we are going to use MySQL DB as a sample. So the first step is to ensure to download the required drivers from the Rexx SQL site so that Rexx programs can work with SQL accordingly. So follow the subsequent steps to ensure that Rexx programs can work with MySQL databases.

Step 1 − Go to the following drivers download page from the Rexx site − https://sourceforge.net/projects/rexxsql/files/rexxsql/2.6/

Step 2 − Download the MYSQL drivers – rxsql26B3_my_w32_ooRexx

Step 3 − Unzip the contents to the local machine.

Step 4 − Add the path of the unzipped folder to the path variable on your machine.

For all the subsequent examples, make sure of the following pointers are in place −

• You have created a database TESTDB.

• You have created a table EMPLOYEE in TESTDB.

• This table has fields FIRST_NAME, LAST_NAME, AGE, SEX and INCOME.

• User ID “testuser” and password “test123” are set to access TESTDB.

• Ensure you have downloaded the mysql jar file and added the file to your classpath.

• You have gone through MySQL tutorial

Database Connection

To establish a database connection, you first need to the Rexxsql DLL and then use the SQLConnect function to establish a connection to the database. The syntax and example of how this can be achieved is given below.

Syntax

SQLConnect(cname,username,password,dbname) 

Parameters

• cname − This is the name to give to the connection.

• username − The user name to connect to the database.

• password − The password to connect to the database.

• dbname − The database schema to connect to.

Return Value

A value equal to 0 will mean that the database connection is successful.

Example

/* Main program */ 
Call RxFuncAdd ''SQLLoadFuncs'', ''rexxsql'', ''SQLLoadFuncs'' 
Call SQLLoadFuncs 
say SQLConnect(c1,'' testuser '','' test123'',''testdb'')

The output of the above program would be as shown below.

0

Creating a Database Table

The next step after connecting to the database is to create the tables in our database. The following example shows how to create a table in the database using Rexx. All of the commands in Rexx SQL are executed by using the SQLCommand function.

Syntax

SQLConnect(sname,statement)

Parameters

• sname − This is the name to give to the statement to execute.

• statement − This is the statement which needs to be executed against the database.

Return Value

A value equal to 0 will mean that the command was successful.

Example

/* Main program */ 
Call RxFuncAdd ''SQLLoadFuncs'', ''rexxsql'', ''SQLLoadFuncs'' 
Call SQLLoadFuncs 

if SQLConnect(c1,''testuser'',''test123'',''testdb'') == 0 then say ''Connect Succedded'' 
if SQLCommand(u1,"use testdb") == 0 then say ''Changed database to testdb'' 
   sqlstr = ''create table employee (first_name char(20) not null, last_name 
   char(20),age int, sex   
   char(1), income float)'' 

if SQLCommand(c2,sqlstr) == 0 then say ''Employee table created''

The output of the above program would be as shown below.

Connect Succedded 
Changed database to testdb 
Employee table created 

Operations on a Database Table

The following types of operations are most commonly performed on a database table.

Performing Transaction

Transactions are a mechanism that ensures data consistency. Transactions have the following four properties −

• Atomicity − Either a transaction completes or nothing happens at all.

• Consistency − A transaction must start in a consistent state and leave the system in a consistent state.

• Isolation − Intermediate results of a transaction are not visible outside the current transaction.

• Durability − Once a transaction was committed, the effects are persistent, even after a system failure.

Here is a simple example of how to implement transactions.

Example

/* Main program */ 
Call RxFuncAdd ''SQLLoadFuncs'', ''rexxsql'', ''SQLLoadFuncs'' 
Call SQLLoadFuncs 

if SQLConnect(c1,''testuser'',''test123'',''testdb'') == 0 then say ''Connect Succedded'' 
if SQLCommand(u1,"use testdb") == 0 then say ''Changed database to testdb'' 
   sqlstr = "DELETE FROM EMPLOYEE WHERE AGE > 20" 

if SQLCommand(c2,sqlstr) == 0 then 
if sqlcommit() == 0 then say committed

The output of the above program would be as shown below.

Connect Succedded 
Changed database to testdb 
COMMITTED

Commit Operation

The commit operation is what tells the database to proceed ahead with the operation and finalize all changes to the database. In our above example, this is achieved by the following command.

Sqlcommit() 

Rollback Operation

If you are not satisfied with one or more of the changes and you want to revert back those changes completely, then use rollback method. In our above example, this is achieved by the following command.

SqlRollback() 

Rexx – Handheld & Embedded Programming

Handheld devices have come a long way and Rexx has a lot of ways in which it can run on these devices. Rexx has support for Pocket PC’s, Palm devices, PDA’s and other smart phone devices. The advantage of Rexx to work on these platforms is that Rexx is really a small weight programming system which just runs in the span of a few kilobytes. Hence it becomes easier to run Rexx programs on these devices.

Rexx on handheld devices can run in the following modes −

• The first mode is the native node where it runs directly on the operating system itself. The advantage on running in this mode is that it is faster since it runs directly off the operating system.

• The next mode is on top of the DOS or emulator program on top of the hand held device. The advantage of this mode is that is can run on any type of operating system as long as the emulator runs on that operating system.

The Rexx Interpreters for the various hand held devices categories are shown below.

• Windows CE − Brexx
• Palm OS − Rexx for Palm OS
• Symbian OS − Regina

For the DOS emulator, the following steps need to be carried out −

Step 1 − First is to download PocketDOS which is a popular DOS emulator. It is designed to run on many operating systems and has support for common VGA screens and serial and parallel ports.

Step 2 − The next step is to download the BRexx files for 16-bit DOS to a Windows PC.

Step 3 − The final step is to use ActiveSync to sync the Rexx program to the handheld device.

There are some other commercial DOS based products available. XTM is a product which falls under this category. The features of this product are as follows −

• Support for the 80186 CPU and instruction set.

• It kind of works off the BIOS code for better performance.

• It can provide emulation for the Math co-processor, version 8087 MPU

• It provides access to the serial ports.

• It supports a variety of languages such as English, French and German.

Rexx – Performance

One of the key aspects of any programming language is the performance of the application. Special practices need to be taken care of to ensure that the application’s performance is not hampered. Let’s look at some of the considerations described in steps for better understanding −

Step 1 − Try to reduce the number of instructions – In Rexx each instruction carries an overhead. So try to reduce the number of instructions in your program. An example of instructions that can be redesigned is shown below.

Instead of using multiple if else statements one can use the parse statement. So like in the following program, instead of having an if condition for each value, and getting the value of word1, word2, word3 and word4, use the parse statement.

/* Main program */  

parse value ''This is a Tutorial'' with word1 word2 word3 word4 
say "''"word1"''" 
say "''"word2"''" 
say "''"word3"''" 
say "''"word4"''" 

Step 2 − Try to combine multiple statements into one statement. An example is shown below.

Suppose if you had the following code which did the assignment for – a and b and passed it to a method called proc.

do i = 1 to 100 
   a = 0 
   b = 1 
   call proc a,b 
end

You can easily replace the above given code with the following code using the parse statement.

do i = 1 for 100 
   parse value 0 1 with 
   a, 
   b, 
   call proc a,b 
end 

Step 3 − Try to replace the do..to loop with the do..for loop wherever possible. This is normally recommended when the control variable is being iterated through a loop.

/* Main program */ 
do i = 1 to 10 
   say i 
end 

The above program should be replaced by the following program.

/* Main program */ 
do i = 1 for 10 
   say i 
end

Step 4 − If possible, remove the for condition from a do loop as shown in the following program. If the control variable is not required, then just put the end value in the do loop as shown below.

/* Main program */ 
do 10 
   say hello 
end

Step 5 − In a select clause, whatever u feel is the best condition which will be evaluated needs to put first in the when clause. So in the following example, if we know that 1 is the most frequent option, we put the when 1 clause as the first clause in the select statement.

/* Main program */ 
select 
   when 1 then say''1'' 
   when 2 then say''2'' 
   otherwise say ''3'' 
end 

Rexx – Best Programming Practices

Every programmer wants their program to be the best when it comes to quality and efficiency. The following are some of the best programing practices or hints when writing Rexx programs which can help one achieve these goals.

Hint 1

Use the address command before you issue any command to the operating system or command prompt. This will help you get the address space beforehand in memory and cause your program to run more efficiently.

An example of the address command is shown below.

Example

/* Main program */ 
address system dir 

The output of the command is as follows, but it could vary from system to system.

Volume in drive H is Apps 
Volume Serial Number is 8E66-AC3D  
Directory of H:  
06/30/2016  01:28 AM    <DIR>          Apps 
07/05/2016  03:40 AM               463 main.class 
07/07/2016  01:30 AM                46 main.nrx 
07/07/2016  01:42 AM                38 main.rexx 
3 File(s)            547 bytes 
Dir(s)  313,085,173,760 bytes free

Hint 2

Ensure all commands to the operating system are in upper case and in quotes wherever possible.

An example for the same is shown below.

Example

/* Main program */ 
options arexx_bifs 
say chdir(''REXXML100'') 
say directory()

When we run the above program, we will get the following result.

0 
D:rexxxml100 

Hint 3

Avoid creating big comment blocks as shown in the following program.

Example

/******/ 
/* */ 
/* */ 
/* */ 
/******/ 
/* Main program */ 
address system dir

Hint 4

Use the Parse statement to assign default values. An example for the same is shown below.

Example

parse value 0 1 with 
a, 
b 

Hint 5

Use the “Left(var1,2)” statement wherever possible instead of the “substr(var1,1,2)” statement.

Hint 6

Use the “Right(var1,2)” statement wherever possible instead of the “substr(var1,length(var1),2)” statement.

Rexx – Graphical User Interface

In order to use the graphic user interfaces available in Rexx, one needs to use 2 packages, one is called ActiveTcl and the other is the Rexxtk package. Along with these 2 packages, one can design normal forms which can have buttons and other controls on the forms.

Environment Setup

The first thing to do is the environment setup. Let’s go through the following steps to have the environment in place.

Step 1 − Download the Activetcl package from the following website − https://www.activestate.com/activetcl

Step 2 − The next step is to start the installation of ActiveTCl. Click on the Next button on the screen to proceed.

Step 3 − Accept the license Agreement and click on the Next button.

Step 4 − Choose a location for the installation and click on the next button.

Step 5 − Choose a location for the installation of the demo’s and click on the Next button.

Step 6 − Click on the Next button to proceed with the installation.

Step 7 − Click on the Finish button to complete the installation.

Step 8 − The next step is to download the Rexxtk software from the following link − https://sourceforge.net/projects/rexxtk/

Step 9 − Double click the installer file from the link in the previous step to start the installation. Click on the next button to proceed.

Step 10 − In the next screen, click on the Yes button to agree to the License Agreement.

Step 11 − In the next screen, choose the location for the installation and click on the Next button.

Step 12 − Choose the Program folder location and click on the next button.

Once the installation is complete, we can now start with programming the GUI’s in Rexx.

Basic Program

Let’s see how we can design a simple basic program with Rexx in a graphical user interface format.

Example

/* Main program */ 
call RxFuncAdd ''TkLoadFuncs'',''rexxtk'',''TkLoadFuncs'' 
call TkLoadFuncs 
do forever 
   interpret ''Call'' TkWait() 
end 
call TkDropFuncs 
exit 0 

The following things need to be noted about the above program −

• The Rexxtk library and all of its functions are loaded using the RxFuncAdd command.

• The do forever loop will keep the window open and will wait for the user input.

• Once the user input is detected, the program will exit.

When the above program is executed, you will get the following output.

Creating Menus

Menus are created with the help of the TkMenu and TkAdd functions. The syntax of these functions are given below.

Syntax

TkMenu(widgetname,options,0) 

Parameters

Widgetname − A name to give to the menu.

Options can be anyone of the following −

• selectcolor − if checkboxes or radio buttons are used as menu options, then this option specifies the color to choose when any menu option is selected.

• tearoff − This option is used for adding sub menus to the main menu.

• title − The string that needs to be used to give the window a title.

Return Value

A handle to the menu created.

Example

/* Main program */ 
call RxFuncAdd ''TkLoadFuncs'',''rexxtk'',''TkLoadFuncs'' 
call TkLoadFuncs 

menubar = TkMenu(''.m1'') 
filemenu = TkMenu(''.m1.file'',''-tearoff'', 0) 
call TkAdd menubar, ''cascade'', ''-label'', ''File'', ''-menu'', filemenu 
call TkAdd filemenu, ''command'', ''-label'', ''Open...'', ''-rexx'', ''getfile'' 
call TkConfig ''.'', ''-menu'', menubar 

do forever 
   interpret ''Call'' TkWait() 
end 
call TkDropFuncs 
exit 0

The following things need to be noted about the above program −

• The menubar is created using the TkMenu function. The ‘tearoff’ parameter means that we need to create submenus which is going to be attached to the main menu.

• We then add 2 menu options called File and Open using the TkAdd function.

When the above program is executed, you will get the following output.

Rexx – Reginald

Reginald is another Rexx interpreter which was developed by Jeff Glantt and has some customizations on how Rexx programs can be run. In this section, we will see how to get Reginald setup and run a few Rexx programs in it.

Environment Setup

The first step is the environment setup which is to download the Reginald files. This can be done from the following website link − http://www.manmrk.net/tutorials/rexx/Reginald/win32/rxusrw32.htm

Once the download is complete and you launch the installer, the next screen will allow you to choose the install location.

Click the Install button to proceed.

Once complete, we can now start to run one sample program in the Reginald interpreter. Create a simple program as shown below.

/* Main program */ 
say ''Hello'' 

Then run the following command −

RxLaunch.exe main.rexx 

You will then get the following output. This program will now be running in the Reginald interpreter.

Other Functions Available

Apart from the normal Rexx commands, Reginald had some specific commands that are tailor-made for the Windows operating system. DriveMap is one such command −

DriveMap

This function gives information on the drive.

Syntax −

Drivemap(,options) 

Parameters −

Options − These are a list of keywords which can be used to get various information on the drives of the local computer.

Return Value

A string value which has information on the drive.

Example −

/* Main program */ 
say ''Drives on system : '' DriveMap(,''FIXED'') 

If the above program is run, you will get the following output. This output depends from system to system.

List of disk drives :  C: D: 

Rexx – Web Programming

Rexx has the facility to work with web servers as well. The most common being the apache web server. In order to use Rexxw with the Apache web server, you need to first download the Rexx modules from the following link − https://sourceforge.net/projects/modrexx/?source=typ_redirect

Once done, make sure to add the mod Rexx modules to the class path.

The following lines need to be added and modified to the Apache configuration file.

The following lines need to be added to the end of the appropriate −

• httpd.conf LoadModule list.
• LoadModule rexx_module modules/mod_rexx.dll

The following lines should be added at the end of the http.conf file.

• AddType application/x-httpd-rexx-script .rex .rexx

• AddType application/x-httpd-rexx-rsp .rsp

• Add these for REXX Server Page support

• RexxRspCompiler “c:/Program Files/Apache Group/Apache2/bin/rspcomp.rex”

Once the above changes have been made, you need to shut down and restart your apache web server.

The above lines also allow you to have Rexx based server pages just like Java server pages. You can add the Rexx code directly to the html pages.

An example is shown below −

<p>The current date and time is 
   <?rexx 
      /* Inserting the rexx statement */ 
      say date() time() 
   ?>
</p>

When a Rexx based server page is run, the following things are carried out −

• First a temporary file is created.

• Then the Rexx Server compiler compiles the file into a Rexx program and places it in the temporary file.

• The next step is to actually run the Rexx program.

Finally, the temporary file is removed.