What should be set term, set output, set term, set term behavior?

[Daniel J S. <dan...@ie...>]

I don't know if anyone put any thought into the proper behavior of 
changing the terminal while some output file is still open, but current 
behavior seems undefined or of no use.  Maybe closing the output after a 
terminal command is the thing to do, but I don't thing gnuplot behaves 
that way.

This has come to my attention because in Octave I'd wondered if there 
was a way to leave a PostScript file or PDF file open, switch over to 
X11 to do some plots, switch back to the PS or PDF terminal and place 
another plot in the file.  (Octave does stem plots as two successive 
plots.)  In other words, in Octave this would be similar to the "print 
-dpdf" command but not closing the file in between plots.

Anyway, back on to behavior.  Try

set term post color solid
set output 'junk.ps'
plot sin(x)
set term x11
plot cos(x)
set term post color solid
replot
set output

OK, what's strange about this is that gnuplot still prints PostScript 
code to the file 'junk.ps' after switching to and back from "set term 
x11".  The content of the file from the first "plot sin(x)" is erased, 
then the result of "replot" is sent to the file.  But then there is the 
additional non-consistency of the PostScript file not being in color as 
indicated by the set term.

As I said before, this is probably undefined.  But I'd think a more 
"defined" or logical behavior would

1) The "set term" causes the output file to be closed as though a "set 
output" had been issued just before "set term"; or
2) The file is not actually closed and it is possible to continue to 
write to the file using a different terminal.  If the user mixes 
incompatible file types, that's his or her problem to clear up.

Alternative 2 would allow plotting in the x11 terminal in an 
intermediate fashion.

Dan