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Lesson 6 The Command Interpreter
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Introduction

Lesson 6 presents two basic uses of the command interpreter:

  • toggling between an editor and the operating system when compiling and linking a program

  • toggling between an editor and the operating system when testing a command file

NOTE: This lesson is primarily for programmers and system managers. You can skip the lesson if you perform neither programmer nor system manager functions.

If you plan to write programs or command files, you will often use the editor to edit the file, keep the file, exit the editor, and return to the operating system to compile and run the program or execute the command file. This process can get tedious when you must do continual editing and error checking. It would be most convenient at such times to be able to toggle between the editor and the operating system; however, pressing the Break key or pressing CTRL Y does not allow you to toggle between the editor and the operating system, and actually execute any commands at the operating system level. So, what does? The command interpreter (CI).

NOTE: It is also possible to toggle by entering :MPE/iX command-name at the editor prompt.

In this lesson, you will learn to do the following:

  • use the CI to toggle between the editor and the operating system when modifying source code or command files

Using the CI

The command interpreter (CI) is the program that acts as the interface between you and the operating system. It checks the MPE/iX commands that you enter for spelling and syntax errors. The CI then passes the command along to the appropriate system procedure for execution. Following execution, control returns to the CI, which becomes ready for another command.

You can run the CI from within the editor and then enter the MPE/iX commands necessary to compile, link, and run a program. Then, by entering EXIT, you can immediately return to the editor. You can also run the CI from within the CI.

NOTE: To run the CI, either the user or the program must have PH capability. The editor does not have PH capability (confirmed earlier with the VERSION command), so the user must have PH capability. To use nested levels of the CI, the user must have PH capability. You can enter SHOWVAR HPCIDEPTH to learn your CI level. When CI is run from the editor, HPCIDEPTH=2. The main CI level (root) is HPCIDEPTH=1.

To run the CI, enter the following command at the editor prompt (/):

:RUN CI.PUB.SYS

or

:XEQ CI

To exit the CI and return to the editor, enter

EXIT

Figure 6-13 The CI

[The CI]

To demonstrate the assistance that the CI can provide you during program development, follow along with the teaching exercise below. If you are a system manager, skip ahead to teaching exercise 5-7.

Teaching exercise 5-6 for programmers: using the command interpreter

  1. There is a C program in your ACCTx account and CLASS group called HIC. You will be compiling, linking, modifying, and running the program using the CI and the editor. It purposely has some hidden bugs in it so that it does not compile successfully the first time that you try to do so.

  2. First, compile and link the program using the command line shown below:

       CCXLLK HIC,HICP

    where:

    • HIC is the source code.

    • HICP is the compiled and linked, executable code.

    • The error listing will appear on the screen and not be stored in a file. (No error listing file was specified in the command line.)

    • When compiling and linking is completed, an END OF PROGRAM message will appear on the screen.

      The general syntax for compiling and linking a program is

         CCXLLK source_code, executable_code[,error_listing]
      NOTE: Since errors do occur during compiling and linking, you will eventually have to modify the source code and correct the errors so that the program will run successfully.

  3. Edit the source file, make the necessary changes, and save the file. The error is clearly noted at the beginning of the source code after the DEFINE section. The correction that you should make is also explained.

       EDITOR

   /T HIC

   /LIST 8/30

    Notice that on or near line 23 there is an error. You can now make the specified changes using standard editing commands (M[ODIFY], R[EPLACE], I[NSERT])

    Now keep the file:

       /K HIC

  4. Toggle back to the operating system by using the CI. Type:

       :RUN CI.PUB.SYS

    or

       :XEQ CI

    Compile and link the program as you did before. It should compile and link without errors.

  5. Run the program by entering the following:

       HICP

  6. The program should prompt you for your logon user name, and then print out the following message:

       Enter your user name>



   HELLO user name



   WELCOME TO THE MPE/iX ADVANCED SKILLS COURSE!



   YOUR CURRENT SEARCH PATH is ***



   TODAY IS date.



   GOOD LUCK!

  7. Return to the editor by entering:

       EXIT

    You should see the editor prompt (/).

    1. Type:

         LIST 80/LAST

    2. Modify the source code on or near line 91 so that the program prints out the current search path. To do this, replace the asterisks (***) in the program's PRINTF search path statement with:

         %s
      NOTE: Don't remove the single quotes, however.

      This indicates that a text string showing the value of HPPATH will be displayed. HPPATH is a system variable that you will learn about in the "Variables and Expressions" module.

    3. Keep the file.

  8. Use the CI again to do the following:

    1. compile and link the program

    2. run the program

    3. return to the editor

  9. EXIT the editor to finish. You should see the system prompt.

    If you exit the CI prematurely by entering BYE instead of EXIT, you will terminate your session. You might also leave behind the editor work file whose name consists of a K followed by a series of digits.

********** End of Exercise 5-6 **********

Teaching exercise 5-7 for system managers:\using the CI

  1. There is a command file in your account called HICOM. You will edit and execute this file using the editor and the CI.

  2. First, execute the command file by entering the following:

       HICOM
    NOTE: An error message results. Eventually, you will have to modify the source code and correct the errors so that the program will run without error.

  3. Edit the command file, make the necessary changes, and save the file. The first line of the file needs a semicolon (;) between USER and PROMPT:

       INPUT USER;PROMPT="Enter user name> "

    To make the change and save the file, follow these instructions:

       EDITOR

   /T HICOM

   /LIST ALL

    Make the necessary change to the first line of the file using the standard editing commands (M[ODIFY], R[EPLACE], I[NSERT]).

    When you are finished making changes, press Enter and keep the file:

       /K HICOM

  4. Toggle back to the operating system by using the CI. Enter:

       :RUN CI.PUB.SYS

    or

       :XEQ CI

    Execute the command file as you did before. The file should prompt you as follows, and then print out the following message:

       Enter your user name>



   HELLO user name



   WELCOME TO THE MPE/iX ADVANCED SKILLS COURSE!



   YOUR CURRENT SEARCH PATH is ***



   TODAY IS date.



   GOOD LUCK!

  5. Return to the editor.

       EXIT

    You should see the editor prompt (/).

    1. Type: 

      LIST ALL

    2. Modify the source code on or near line 7 so that the command file prints out the current search path. To do this, replace the asterisks (***) in the search path ECHO statement with:

         !HPPATH

      This indicates that a text string showing the value of HPPATH is to be displayed. HPPATH is a system variable that you will learn about in the "Variables and Expressions" module.

    3. Keep the file and then use the CI again to execute the command file. The message that you receive should now display a search path.

      You can also execute the command file by entering

         :XEQ HICOM

    4. Return to the editor and then leave the editor 

      EXIT
      to finish.

********** End of Exercise 5-7 **********

Lesson summary

  1. The command interpreter (CI) provides a quick way to toggle between the editor and the operating system.

  2. The command line :RUN CI.PUB.SYS (or :XEQ CI) lets you use the CI from the editor; EXIT returns you to the previous level of the CI (in this lesson, usually the editor).

  3. The CI is useful when writing and testing programs or command files.



Lesson 5\using Parameters
 		  


Chapter 7 Module 6: Variables and Expressions