TOPS-20 Commands Reference Manual
BACKSPACE
Moves a magnetic tape set backward over a specified number of files or records.
Format
@BACKSPACE (DEVICE) dev: n units
where:
| dev: | is the name of the tape set or magnetic tape drive that you want to move backward. The colon after the device name is optional. |
| n | is the number of files or records over which you want to backspace.
Default n - 1 |
| units | is either FILES or RECORDS.
Default units - FILES |
Restrictions
BACKSPACE with Open Files
If you have given a CTRL/C to exit from a program that has opened a magnetic tape drive and you then give the BACKSPACE command for that tape drive, the system will first ask if you want to close the associated file. You must do so for BACKSPACE to succeed, but you will probably be unable to continue the program from that point because the file will now be closed.
RECORDS Argument Used for Unlabeled Tapes Only
You cannot give the RECORDS argument to the BACKSPACE command when using a labeled tape, because read and write operations for labeled tapes always move the tape to the beginning of a file first.
Related Commands
| SKIP | for moving a magnetic tape set forward |
| REWIND | for backspacing a tape volume or tape set to its logical beginning (the beginning of the first file) |
| UNLOAD | for completely rewinding a magnetic tape onto the source reel |
Examples
Backspace your magnetic tape one file.
@BACKSPACE MTA0: 1 FILE