Lesson 2 Naming Conflicts

• Use the HELP command to check for duplicate file names before naming a file.

• Use the MPE/iX system command XEQ.

The MPE/iX system tries to interpret everything that you type at the prompt as an instruction of some kind. This includes MPE/iX system commands, programs, utilities, subsystems, and user-created executable files, such as command files.

If you are a new user of the MPE/iX system, you certainly cannot know all of the instructions that MPE/iX will accept. But you should always try to keep your file names from duplicating the names of other commands on the system.

Before you name a command file, check with the system first to see whether the name that you want for your command file is already in use.

Use the help facility to do this.

At the MPE XL prompt, enter:

   HELP showvarReturn

Since there is a SHOWVAR MPE/iX system command, you get the help facility display.

   :SHOWVAR



      Displays specific variable names and their current values, (NEW)



   SYNTAX



      :SHOWVAR [varid][,varid]...[,varid]

Enter:

   HELP PSReturn

Something like the following appears on the screen if your proposed file name matches the name of another executable file on the system.

   :HELP PS

   USER DEFINED COMMAND FILE:  PS.ETHEL.MERTZ



   PR

   st

Try it.

Something like this appears on the screen if your proposed file name matches a program file (or subsystem/utility) on the system.

   HELP sortReturn

   PROGRAM FILE:  SORT.PUB.SYS

The SORT command is an instruction already in the system. Saving your command file as SORT would be pointless.

Try the name GLOBAL:

   HELP globalReturn

        ^

   Can't find anything under this command or in table of contents.

You see this message if the name that you select is unique to the system.

You could, therefore, keep a command file called GLOBAL and successfully execute it without getting surprising results, but...there is always an exception.

	NOTE: Some kinds of executable files can be protected with various forms of security. And one of those forms of security can hide the file name from the help facility. In such a case, you might be fooled into thinking that the file name you want to use is unique and available for use.

The MPE/iX command XEQ bypasses system commands, programs, utilities, and subsystems and executes command files -- even in the case of name duplication.

Try executing your SHOWVAR command file using the XEQ command:

   XEQ showvarReturn

This time your command file called SHOWVAR should execute and display the output from its one command, LISTFILE @.@.

Using XEQ along with your command file name does avoid potential naming conflicts, but renaming your command file to avoid naming conflicts also avoids any confusion over the purpose of two identically named, executable files.

1. If you had a command file called RUNIT, what would you type at the system to execute it?

2. If RUNIT was also the name of an MPE/iX command, how would you execute your command file RUNIT from question 1?