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Defaulted or Omitted Parameters [ Understanding Your System ] MPE/iX 5.0 Documentation


Understanding Your System

Defaulted or Omitted Parameters 

When you enter a command line, the operating system examines everything
that you typed up to the point at which you pressed Return.  If you have
not mistyped the name of the command, or any of its parameters, the
operating system searches its memory concerning the command that you
entered.

The operating system executes a series of tests to determine how to
execute the command:

   *   If the command is PURGE, look up the parameters of PURGE, and 

          *   If a file is named, look for the file, and 

                 *   If the file exists, determine whether ,TEMP is
                     specified, and 

                        *   If ,TEMP is specified, then erase a temporary
                            file; otherwise, erase a permanent file

This description is an over-simplification, but it illustrates the kind
of "reasoning" that the computer follows when it tries to execute a
command that you enter.

For every parameter of every command, there is an otherwise that tells
the computer what to do if the following occurs:

   *   The user decides to ignore an optional parameter.

   *   The user fails to enter a required parameter.

   *   The user simply mistypes the command or one of its parameters.

In this case, the otherwise of ,TEMP is:  "erase a permanent file, if it
can be found."

The otherwise (default) for a required parameter that you fail to
specify, that you mistype, or that the computer cannot, for some reason,
accept is to display an error message.

     :PURGE
            ^
     REQUIRES FILE NAME TO BE PURGED.  (CIERR 381)

CIERR 381 identifies the error that the system encountered.  It was a CI
(command interpreter) error, an error made when the command interpreter
attempted to carry out this instruction.  It was error number 381 in the
catalog of errors that the system recognizes and reports.

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MPE/iX 5.0 Documentation