Command Parameters

Simple commands, such as SHOWME and SHOWTIME, need--and want--nothing more from you than this: type the name of the command and press Return.

   SHOWMEReturn



   SHOWTIMEReturn

The complex commands offer greater flexibility in their execution, but this flexibility comes at a price. The complex command may require additional pieces of information from you in order to execute successfully.

The pieces of information that you add to a command are called parameters. You add pieces of information after typing the command name and before pressing Return. The PRINT command accepts a parameter, the name of a file:

   PRINT filenameReturn

Using italics here (filename) indicates that you would have to substitute the name of an existing file where filename appears, as in this example:

   PRINT TAXJANReturn




	TIP: Taken together, `PRINT TAXJANReturn` make up a command line--a line consisting of a command, plus its parameters (if any), terminated by Return. You might think of a command line as a package of instructions for the computer. Use the `PRINT` command. Use it on the `TAXJAN` file. Return ties up the package and sends it to the computer.

A command gives instructions to the computer. In the same way, parameters give instructions to a command. Parameters control or modify the way in which the command executes.

Some commands accept only one parameter. Some accept many parameters.

Parameters fall into these two groups:

Required parameters
A required parameter is a piece of information that you must add to the command in order to have the command execute.
Optional parameters
An optional parameter is a piece of information that you may choose to add to the command. Add the information if it suits your purpose.
Be aware, though, that choosing not to include an optional parameter will cause the computer to do something. What will it do? That depends upon which command you are using. The LISTFILE command is an example.

Optional parameters

LISTFILE commands accepts several parameters, but all of them are optional.

   LISTFILEReturn

Used without any of its optional parameters, LISTFILE displays the names of all of the files in the group where you are logged on. That is the action that this command takes when you do not specify any of its parameters.

Suppose, instead, that you want to see only the names of those files that begin with the letter "G." If that is what you want, add one parameter to the LISTFILE command line:

   LISTFILE G@Return

Table 7-1 Wildcard Characters: @ ? #

Character	Meaning
@	This tells the computer to look for any combination of letters or numbers (none or as many as 8). In this case `G@` tells the computer to look for any file name in your logon group that begins with the letter `G`
?	This is the equivalent of "any single character, letter or number." `G??` tells the computer to look for any file name beginning with the letter "G" and having (at most) two more letters or numbers in the name.
#	This is the equivalent of "any single number (digit) 0 through 9."




	TIP: `@#?` translates to "any name beginning with any combination of letters or numbers that ends in a single number followed by a single letter or digit." Files called `FIN2A`, `ACCT33`, and `TAXRPT2G` would fit the specification described by `@#?`. Files called `FINAL2` or `ACCTS3` would not fit the specification.

Adding the parameter G@ permits you to narrow the search for file names to the ones you wanted--file names beginning with "G."

Recall that LISTFILEReturn by itself gives you all of the file names in your logon group. Why does it do that?

The programming engineers who created the LISTFILE command knew that someone using LISTFILE would want to see the names of files, but which files? They had no way of knowing what you might choose, so they made two decisions.

The first decision was to leave the choice to you--the parameter for specifying files is optional. You choose. The second decision concerned what LISTFILE should display if you make no choice at all.

This second decision involved creating a default--a set of instructions for LISTFILE to follow if the user does not specify any parameters. By default, LISTFILE lists all the file names it can find in your current group if you decide not to narrow the search. With this release, LISTFILE contains additional parameters. For more information, refer to the book, New Features of MPE/iX: Using the Hierarchical File System (32650-90351).

Every optional parameter of a command has some default action. You will find information about optional parameters and their defaults in book Commands Reference - HP 300 Series 9X8LX (B3813-90011), and under the Parameters heading, of each command in the &help;.

Required parameters

In contrast to optional parameters, required parameters are pieces of information that you must give to a command in order to have the command execute successfully.

The command to remove or erase a file, PURGE, requires that you supply at least one parameter, the name of the file to be removed:

   PURGE ACCTRPTReturn

This use of PURGE removes the file called ACCTRPT from the group in your logon group. For PURGE, the name of some file is a required parameter.

If you accidentally omit the name of a file to be purged, the operating system will display an error message informing you of your mistake. This is true of any required parameter of any command. Omitting required information from the command line generates an error message.

How do I find out which parameters go with each and every command? Two sources of information are readily available:

Commands Reference - HP 3000 Series 9X8LX (B3813-90011)
the MPE/iX Help Facility
The MPE/iX Commands Reference Manual, Vols I and II (32650-90003), a comprehensive manual that includes details on all MPE/iX commands.

Command Parameters

Technical documentation

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Optional parameters

Required parameters