Save command line output to variable in Fortran

Question

Is there a way to store the output of a command line utility to a variable in Fortran?

I have a BASH based utility which gives me a number which needs to be used in a Fortran program. I want to call the utility through the program itself, and avoid writing the output to a file if possible.

Something like this maybe?

integer a
write(a,*) call execute_command_line('echo 5')

Or like this maybe?

read(call execute_command_line('echo 5'),*) a

I don't think either of these is right though. I would like to know if there is actually a method to do this. I read the docs for execute_command_line but I don't think there is an output argument for the subroutine which does this.

Answer 1

Since you're using BASH, lets assume you're working on some kind of unix-like system. So you could use a FIFO. Something like

program readfifo
  implicit none
  integer :: u, i
  logical :: ex
  inquire(exist=ex, file='foo')
  if (.not. ex) then
     call execute_command_line ("mkfifo foo")
  end if
  call execute_command_line ("echo 5 > foo&")
  open(newunit=u, file='foo', action='read')
  read(u, *) i
  write(*, *) 'Managed to read the value ', i
end program readfifo

Note that the semantics of FIFO's wrt blocking can be a bit tricky (that's why there is the '&' after the echo command, you might want to read up on it a bit and experiment (particularly make sure you haven't got a zillion bash processes hanging around when you do this multiple times).