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From: tswingle@oucsace.cs.OHIOU.EDU (Tom Swingle)
Newsgroups: comp.lang.pascal
Subject: Re: Redirecting Exec() output
Message-ID: <3249@oucsace.cs.OHIOU.EDU>
Date: 29 Apr 91 20:28:51 GMT
References: <26614@adm.brl.mil> <2684@umriscc.isc.umr.edu>
Followup-To: comp.os.msdos.programmer
Organization: Ohio University CS Dept., Athens
Lines: 71

In article <2684@umriscc.isc.umr.edu> bkirby@mcs213f.cs.umr.edu (Bill Kirby) writes:
>In article <26614@adm.brl.mil> nate@neutron.lcs.mit.edu writes:
>>Craig,
>>

[ CRT unit discussion deleted ]

>I posted a reply to the original question, but I have not seen it here
>yet.  I am having the same problem.
>
>In any case, the above code is not relevant to our problem.  Yes, you
>need to open the file as described above if you want your pascal program
>to output to standard out.  We want to Exec a program from within
>pascal and have the output redirected to a file.
>
>For instance, suppose I have a program HELLO.EXE (not necessarily
>written in pascal) which outputs "hello, world" to standard out.  
>At the DOS prompt I can type "HELLO > OUTPUT.TXT" and a file 
>OUTPUT.TXT will be created containing the text "hello, world".
>
>Now, if you try the following from within a pascal program:
>
>     Exec("COMMAND.COM","/C HELLO.EXE > OUTPUT.TXT");         
>
>it should produce the exact same results, but it doesn't.
>Redirecting INPUT in this manner works fine.
>
>Am I doing something wrong?
>
>BTW, I'm using Turbo 6.0.
>
>Thanks,

I think the problem lies in the fact that Turbo Pascal removes all references
to redirection since it is not set up to support redirection.  I had posted a
solution like the one above but now that someone has tested and mentions that
it does not work, I think I see why.  Turbo Pascal sees the line

     Exec("COMMAND.COM","/C HELLO.EXE > OUTPUT.TXT");         

and sees that it is a command being executed with redirection.  Since Turbo
Pascal doesn't support redirection, it removes the redirection so the line
becomes

     Exec("COMMAND.COM","/C HELLO.EXE");         

If you could trick Turbo into passing the "> OUTPUT.TXT" to Dos, you could 
probably get this to work, but I don't know of any way to do it.  One solution
posted was to create a DUMMY.BAT file containg the line

     HELLO > OUTPUT.TXT

and use the line

     Exec(getenv('comspec'),"/c DUMMY.BAT");

of course, this is a very poor programming solution because anyone using your
program would have to have DUMMY.BAT in the current directory or in the PATH,
and if you wanted to change the program being executed you would have to 
change the .BAT file; it would not be a very self-contained solution.  The only
other thing I can tell you is to see if someone has written an EXEC procedure
supporting redirection, or if you are familiar with how it is done, write it
yourself.  I'm not familiar enough to know how this is done.  Perhaps you
could post this question to comp.os.msdos.programmer and they would be more
helpful.  I am redirecting :-) followups there so that it might be likely to
get an answer.
 
-- 
"The problem you are experiencing is  |  "To be sure of hitting the target, 
not with the network nor with the     |  shoot first and, whatever you hit, 
station.  Please adjust your set."    |  call it the target."