PRINT--A Closer Look

The syntax diagram for the PRINT command is a little more complex than the ones illustrated so far. It looks like this:

   PRINT[ [FILE=]filename][;[OUT=]outfile]

	TIP: This is only part of the syntax diagram for PRINT. It has other parameters, in addition to the ones shown here

The filename parameter is optional.

Notice, though, that you have the choice of whether to precede that parameter with FILE=. (Within MPE/iX, there are historical and engineering reasons for making this option available.)

The parameter outfile is optional, and so is the decision whether to precede it with OUT=. Look carefully: the semicolon is required if you choose to specify an outfile.

What is an outfile? It is an optional parameter. It permits you to specify the destination for the contents of filename. Because it is an optional parameter, outfile has a default action--in this case, a destination for the contents of filename if you decide not to specify a destination.

The default destination is your video screenl. From the computer's point of view, your terminal is a file, too.

Suppose that you tried this:

   PRINT TAXJAN;XYZReturn

What happens?

You have specified an outfile, so the contents of the file will not go to the video terminal.

In this situation, the computer obligingly creates a temporary file called XYZ. You could find it with LISTFILE @;TEMPReturn. This file will disappear as soon as you log off.

You could transform this temporary file into a permanent file by using the SAVE command:

   SAVE XYZReturn

	Worth Knowing: PURGE removes only one file at a time: PURGE G@Return will not remove all of the files beginning with the letter "G." It will, instead, generate a message informing you that you made an error. You must use PURGE each time that you wish to remove a single file. That helps to ensure that you make a conscious decision to erase a particular file. MPE/iX has no command to "un-erase" a file. Backing up files is vital. You can bring back a file from tape by using the RESTORE command if the file was copied to tape with the STORE command, but that does not help if the file that you erased has not been recorded on tape. Regular and frequent backups give you the best protection against the inadvertent erasure of a file.