HP 3000 Manuals

MPE V to MPE XL: Getting Started

Lesson 2:  Comparing User Commands 

Those of you who create your own UDC files will notice some similarities
between UDC files and command files.  The comparisons on the next few
pages will help you weigh the benefits of having both UDC files and
command files available in MPE XL.


NOTE  For this lesson, recall the distinction between the terms UDC file
      and UDC. A UDC file is an MPE file that contains one or more UDCs
      separated by asterisks.  In order to use the UDCs, the file must
      first be cataloged using the SETCATALOG command.

      A UDC is not an MPE file.  It is contained within a file, and it
      consists of one or more MPE commands and/or user commands.  The UDC
      executes when its command header is typed at the prompt, if the
      file in which it resides has been cataloged.  For more information
      on UDCs, refer to the MPE XL General User's Reference Manual 
      (32650-90002).


          Content Considerations 

A UDC File:                                 A Command File: 

Contains one or more UDCs.  Each UDC begins Contains no command header; contains one or
with an obligatory command header and one   more option headers (optional), followed by
or more option headers (optional), followed one or more executable commands.
by one or more executable commands.  Each
UDC is separated from the other UDCs in the
file by one or more asterisks (*).


Users should be aware of a key difference between UDCs and command files
in the area of maintenance.

          Maintenance Consideration 

A UDC File:                                 A Command File: 

The UDC file must be cataloged, using the   A command file is not cataloged.  It can be
SETCATALOG command.                         modified and purged easily.

An example of a UDC file follows:
____________________________________________________________________
|                                                                  |
|                                                                  |
|      :SETCATALOG myudc                                           |
|                                                                  |
|      :SHOWCATALOG                                                |
|                                                                  |
|      MYUDC.PUB.MERTZ                                             |
|         GREETING     USER                                        |
|         PRINTIT      USER                                        |
|         ST           USER                                        |
|                                                                  |
____________________________________________________________________

Exercises 

4.   True or false:  A command file may be cataloged, but does not have
     to be.

5.   True or false:  When you enter a command file name, everything in
     the file is executed.

A comparison of execution of the files follows:

          Execution 

A UDC:                                      A Command File: 

Is invoked at the prompt by its command     Is invoked at the prompt by its file name.
header.

Has the option of being invoked when the    Logon option ignored.  However, it may be
user logs on to the system (OPTION LOGON).  called upon by a logon UDC. (See SHOWME
                                            below.)

Should be used for frequently used, stable  Can be used to test potential UDCs.  Should
commands.                                   be used when contents change frequently.



NOTE  Parameters can be defined in UDCs and command files, using a PARM
      statement defined in the user command opening line.  Refer to the
      MPE XL General User's Reference Manual (32650-90002).


Exercise 

6.   For each item below, put an X in the appropriate column(s) to show
     whether the item is a characteristic of UDCs, command files, or
     both.

MPE/iX 5.0 Documentation