The FDROP function deletes one or more
components from the start or end of the file, without renumbering the remaining
components. The syntax is:
FDROP TIENO N {PASS}
TIENO is the tie number you used to tie or create
the file (or the tie number returned by APLX if you tied or created it using 0
instead of your own tie number). If you
tied the file using a pass number, you must provide the same pass number, as
the PASS parameter.
The parameter N is a positive or negative
integer. If it is positive, the first N
components of the file are deleted. If
it is negative, the last -N components are deleted. In both cases, existing components are not
re-numbered.
For example, suppose you have a file with components
numbered from 1 to 12. After executing the two statements:
FDROP TIENO,2 FDROP TIENO, ¯3
the first component in the file will be component 3, and the
last will be component 9. The original
components 1, 2, 10, 11, 12 will no longer exist. The original components 3 through 9 still exist, and retain the same component numbers.
See also the function FDELETE which
deletes a single component anywhere in the file, re-numbering the remaining
components accordingly.