Contents of file named thedoubler.f90

program thedoubler
   use sacio90 ! import the SACIO90 module
   implicit none

   type (SAC1) :: trace ! SAC time-series file structure

   ! Read in the data file
   call sacio90_read('data.sac',trace)

   ! double all data points
   trace % y(1:trace % npts) = & 
      trace % y(1:trace % npts) * 2.0
   
   ! set a user character header 
   trace % kuser0 = 'DOUBLED!'

   ! write the altered file back to disk under
   ! a different name.
   call sacio90_write('doubled.sac',trace)
end program thedoubler