! This file: http://ftp.aset.psu.edu/pub/ger/fortran/hdk/prepend.f90
!
 Program Prepend
! Illustrate how to prepend data to an existing file without copying it.
! F-Compiler compatible.
! H. D. Knoble, hdkLESS at SPAM psu dot edu, 20 July 2003.
!
   Character (Len=40) :: line, File1, File2
   Integer :: j, ios
   File1="PREPEND.DAT"
   File2="EXISTING.DAT"

! Process the data to be prepended.
   open (unit=50,file=file1, action="READ", status="OLD", position="REWIND")
   j=0
   do
     read(unit=50,fmt="(A)",iostat=ios) line
     if (ios == 0) then
       j=j+1
       write(unit=*,FMT=*)"Record#",j,":",line
     else
       exit
     endif
   end do
   close(50)
   print *, "Total records prepended=",j

! Process the existing data.
   open (unit=50,file=file2, action="READ", status="OLD", position="REWIND")
   do
     read(unit=50,fmt="(A)",iostat=ios) line
     if (ios == 0) then
       j=j+1
       write(unit=*,FMT=*)"Record#",j,":",line
     else
       exit
     endif
   end do
   close(50)

   print *, "Total records processed=",j
end program prepend