[Arjen Markus] This page is meant to elaborate the management of interactive For
tran programs via Tcl.

''Note:'' Very sketchy right now - I want to get the information available

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Below is a simple example:
   * Tcl asks for a string and puts it to an executable program written in Fortran.
   * This program reads the string and writes it out, until the string is "q", then it exits.
   * At this moment, Tcl must exit too.

The trick is to use file events to handle the buffering and broken pipe issues correctly and to use the non-standard Fortran routine flush() to flush the output buffers.
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The Tcl code:

   global inout
   set inout [open "|copy_inp" "w+"]
   fconfigure $inout -buffering none

   puts "Input:"
   fileevent $inout readable {
      gets $::inout copied
      puts $copied
      if { [eof $inout] } { close $inout; set forever 1 }
   }
   fileevent stdin readable {
      gets stdin line
      puts $::inout $line
      puts "Input:"
   }
   vwait forever

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The Fortran code:

   !  copy_inp.f90 --
   !     Copy stdin to stdout - IPC test
   !
   program copy_inp
      ! Compaq Visual Fortran requires:
      ! use dflib

      character(len=60) :: string

      do
         read(*,*)  string
         write(*,*) 'Copied: ', string
         call flush( 6 )

         ! On SGI use:
         ! call flush( 101 )

         if ( string .eq. 'q' ) stop
      enddo
   end program

''Notes:''

   * Standard output is usually unit 6, but on SGI it is unit 101
   * As FLUSH() is non-standard, you may need to add a USE statement, or link with a special library

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See also: [open], [exec], [Inventory of IPC methods]