Due to historical reasons, have a long formated sequential (text) file of
data. Need to re-write one of the early header cards. Tried the open and
rewrite scheme below, but rest of file disappears after rewriting the
required line.
So, short of copying the rest of the file, how can one do this?

File needs to be sequential & formated:

The open is

open( iU, file = cFileName )
write(iU,'(a)') ' VERSION_1 '

write(iU,'(a)') ' some text'

write(iU,'(79a)') cTitle


write(iU,*) rReal, iDum1, iDum2, iDum3

write 1000's of lines of data.



Now, need to change line 4 and keep all data following line 4. The
following deletes all data after line 4.

rewind( iU )


do i = 1, 3

read(iU,*)

enddo


read(iU,*) rReal, iDum1, iDum2, iDum3

backspace(iU)


iDum3 = iNewValue ! change parameter value


write(iU,*) rReal, iDum1, iDum2, iDum3

close(iU)

So, how to change only one line of this data file without reading /
rewriting the entire file.

Thanks.