Re: bidirectional pipe by Spawn on UNIX

[fireman(at)mcst.gsfc.nasa.gov (Gwyn Fireman)]

Ivo Labbe (ivo@strw.leidenuniv.nl) wrote:
: While writing to an piped shell process from IDL in an unix environment
: goes fine, I seem to be unable to read from it. Type conversion errors
: all over the place. I'm obviously doing something wrong and IDL help is
: not explicit on the subject. What is the preferred way to read the
: output from a spawned piped child process?

Variables read from a bidirectional pipe must be declared with the
correct in advance.  Strings must be of the correct length.  I have a
Fortran example below (well, it worked 4 years ago, anyway :)

pro demo, mult, out, colors

mult	= fix(mult)			; make sure multiplier is integer
in	= indgen(10)			; initialize input array
out	= in				; initialize output array
colors	= replicate('0123456789', 7)	; initialize string array

spawn, 'demo', unit = lun		; open bi-directional pipe
printf, lun, in, mult, out		; pass variables to pipe
readf,  lun, in, mult, out, colors	; get variables from pipe
free_lun, lun				; close bi-directional pipe

return
end

C	compile using "f77 -o demo demo.f"

	program demo

	implicit none
	integer in(10), mult, out(10), i
	character*10 colors(7)

C
C	Read input parameters
C
	read *, in, mult, out

C
C	Calculate output array
C
	do 10 i = 1, 10
	  out(i) = in(i) * mult
10	continue

C
C	Define character array
C
	colors(1) = 'red'
	colors(2) = 'orange'
	colors(3) = 'yellow'
	colors(4) = 'green'
	colors(5) = 'blue'
	colors(6) = 'indigo'
	colors(7) = 'violet'

C
C	Print output parameters
C
	print *, in, mult, out

	do 15 i = 1, 7
	  print *, colors(i)
15	continue

	stop
	end


--
-- Gwyn F. Fireman
-- General Sciences Corporation / MODIS Characterization Support Team
-- Gwyn.Fireman@gsfc.nasa.gov   301-352-2118