From octave-maintainers-request at bevo dot che dot wisc dot edu Mon Dec 15 17:56:43 2003
Subject: capture command output
From: Paul Kienzle <pkienzle at jazz dot ncnr dot nist dot gov>
To: octave-maintainers at bevo dot che dot wisc dot edu
Date: Mon, 15 Dec 2003 18:56:17 -0500

Hi,

For a few reasons, I want to be able to run
a command and capture its output without it going
to the screen.  One is for parallel octave --- if
you execute stuff on another processor, you want
to be able to send the screen output back to the
controlling terminal.  Another is for embedded
octave --- if you execute an octave command in
tcl/tk, you want to be able to put its output in 
a tcl/tk window.  A third reason is testing ---
I want to be able to run the test example and 
display a summary on the screen and have the 
results in a file.

Using pager tricks, I can hack this (see the 
"capture" command below), but I would rather
not go through the file system.  

Having written a few DLD functions, I know that all
screen output goes through octave_stdout.  I was 
assuming this was simply a variable that I could 
cache, replace with a my own stream, and restore when 
I was done.  Alas, it is 

  #define octave_stdout (octave_pager_stream::stream ())

and of course the interesting bits of the class
octave_pager_stream are private.

Any suggestions how we can do this from C++ and from
the script level?

Error messages can already be buffered, but warnings
cannot.

Thanks,

Paul Kienzle
pkienzle at users dot sf dot net

PS, Is there any way to override 'private'?  E.g.,
by having your own copy of the header files with the word
private replace by public whereever it occurs?  Or does the
C++ ABI do something special when storing privates?


function [ ret ] = capture (cmd)

   pso = page_screen_output;
   pager = PAGER;
   poi = page_output_immediately;
   tmpfile = sprintf("/tmp/capture%d",getpid);

   unwind_protect
     PAGER = ["cat >",tmpfile];
     page_screen_output = 1;
     page_output_immediately = 1;
     evalin('caller',cmd);
   unwind_protect_cleanup
     PAGER = pager;
     page_output_immediately = poi;
     page_screen_output = pso;
   end_unwind_protect

   pause(0.1);
   fid=fopen(tmpfile,"r");
   ret = setstr(fread(fid, Inf, "char")');
   fclose(fid);
   unlink(tmpfile);

endfunction