data.txt

nx=128
ny=128
nz=128

dataread.f90

program dataread
  implicit none
  integer nx, ny, nz, i, n
  character(100) line

  type::params
    character(32)::name
    character(32)::val
  end type params
  type(params),dimension(:),allocatable::test

  open(17, file='data.txt', status='old')
  allocate(test(100))

  do
    read(17, '(A)', end=100) line
    i = i + 1
    call splitTextByEqual(line, test(i)%name, test(i)%val)
  end do
  100 print*, 'Data inputted.'

  n = i !record number

  do i=1, n
    if(test(i)%name == 'nx') read (test(i)%val, *) nx
    if(test(i)%name == 'ny') read (test(i)%val, *) ny
    if(test(i)%name == 'nz') read (test(i)%val, *) nz
  enddo

  print '(" nx, ny, nz = ", 3(i0, ", "))', nx, ny, nz

  contains
    subroutine splitTextByEqual(txt, name, val)
      implicit none
      character(32) txt,name,val

      name = txt(:(index(txt, '=') - 1))
      val = txt((index(txt, '=') + 1):)
      
    end subroutine splitTextByEqual

end program