HP 3000 Manuals HP 3000 Manuals
Lesson 4 Deleting Files
Lesson 4 presents deleting files.
* the command to erase a file: PURGE
* recovering from an accidental file erasure
The PURGE command
The PURGE command erases a file. It erases only one file at a time. If
you want to erase five files, you need to use the PURGE command five
times.
Make sure that you are in the home group of your account. Recall from
module 4 that the LISTUSER command shows which group is designated as
your home group.
Enter:
LISTUSERReturn
NOTE LISTUSER does not tell you which group you are currently in. It
tells you only which group is designated as your home group.
To find out which group you are currently in, use the SHOWME command.
Enter:
SHOWMEReturn
Use CHGROUP if necessary get into your home group.
To purge the file called NEWDRAFT, enter:
PURGE NEWDRAFTReturn
Use LISTFILE to make sure that NEWDRAFT has been removed.
Now erase NXTDRAFT in the same way.
PURGE NXTDRAFTReturn
If you try to erase a file that does not exist, you get an error message.
Try to erase the file QZQXQZ. What happens? (Of course, if the file does
exist, it is erased. MPE/iX assumes that you know what you want to do
when you issue a command.)
Recovering a file
The day will come when you accidentally erase a file that you need. It
happens to almost everyone at some time.
MPE/iX does not provide an unerase command. MPE/iX assumes that you knew
what you were doing when you erased a file.
There is a remedy. Your system operations personnel should perform
regular system backups (storing all of the files on the system to tape).
* If you created the file after the last backup, you cannot retrieve
the file.
* If you created the file before the last backup, you can restore
the file to the computer.
* If you created the file before that last backup but you modified
it after the last backup, you can restore the earlier version of
the file; however, the modifications are lost.
For this exercise, suppose the following:
* Your system operator regularly backs up files on the system every
day at 6:00 P.M.
* You made changes to MYFILE yesterday (Monday).
* Today is Tuesday, 11:00 A.M.
* You have been working on MYFILE all morning.
* You accidentally erased MYFILE five minutes ago.
What would you do?
* Ask your system operator to have MYFILE restored to the group and
account where it belongs.
What is restored?
* All of the changes made to MYFILE on Monday are restored. (The
backup was performed at 6:00 P.M. yesterday.)
* You have lost the work that you did today (Tuesday), and you need
to reenter those changes.
How much work is lost depends on two things:
* how much time has passed since you made changes to the file and
kept it
* how much time has passed since the files on your system were
stored to tape in a backup
NOTE System operation departments have different backup schedules, but
all should perform regular file backups. Find out from your
manager or system operations department what the backup schedule
is. One day you may need to know.