Fortran find string in txt file

Question

I would like to know how to find a string in a txt file and read the numbers after it. The txt portion of the file is like:

...
x0 1 0 1 0.5 0
dx0 0 0 1 0 0


        

Answer 1

The program below shows how to read numbers from a line where the search string is the first word. It uses an internal read, which is often useful in Fortran I/O.

program xinternal_read
implicit none
integer :: ierr
integer, parameter :: iu = 20
character (len=*), parameter :: search_str = "dx0"
real :: xx(5)
character (len=1000) :: text
character (len=10) :: word
open (unit=iu,file="foo.txt",action="read")
do
   read (iu,"(a)",iostat=ierr) text ! read line into character variable
   if (ierr /= 0) exit
   read (text,*) word ! read first word of line
   if (word == search_str) then ! found search string at beginning of line
      read (text,*) word,xx
      print*,"xx =",xx
   end if
end do
end program xinternal_read

The output is

xx = 0. 0. 1. 0. 0.