12.1 BACKSPACE Statement

The BACKSPACE statement positions a sequential file at the beginning of the preceding record, making it available for subsequent I/O processing. It takes one of the following forms:

 BACKSPACE ([UNIT=]io-unit [,ERR=label] [,IOSTAT=i-var])
 BACKSPACE io-unit
Is an external unit specifier.
Is the label of the branch target statement that receives control if an error occurs.
Is a scalar integer variable that is defined as a positive integer if an error occurs and zero if no error occurs.

Rules and Behavior

The I/O unit number must specify an open file on disk or magnetic tape.

A BACKSPACE statement must not be specified for a file that is open for direct, append, or keyed access, because record n is not available to the RMS I/O system.

If a file is already positioned at the beginning of a file, a BACKSPACE statement has no effect.


The following statement repositions the file connected to I/O unit 4 back to the preceding record:


Consider the following statement:


This statement positions the file connected to unit 9 back to the preceding record. If an error occurs, control is transferred to the statement labeled 10, and a positive integer is stored in variable IOS.

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