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From: mcvoy@uwvax.UUCP
Newsgroups: comp.unix.questions,comp.unix.wizards,comp.lang.c
Subject: Re: Filtering Everything
Message-ID: <3446@rsch.WISC.EDU>
Date: Sun, 12-Apr-87 17:00:17 EST
Article-I.D.: rsch.3446
Posted: Sun Apr 12 17:00:17 1987
Date-Received: Tue, 14-Apr-87 00:08:57 EST
References: <919@watmum.UUCP> <6447@bu-cs.BU.EDU>
Reply-To: mcvoy@rsch.WISC.EDU (Larry McVoy)
Distribution: comp
Organization: U of Wisconsin CS Dept
Lines: 36
Xref: utgpu comp.unix.questions:1690 comp.unix.wizards:1752 comp.lang.c:1579

(Someone) asks:
>>I wish to write a program in C that I can somehow set up so all output
>>to my terminal goes through it first, and all input from my terminal goes
>>through it too.

(Barry Shein) writes:
>On 4.2/4.3 you want to do this via pty's. The script program is almost
>
>On SYSV I think you'll have difficulties doing what you say, especially
>for terminal oriented programs (you mention vi.)

Barry is quite right here (right, right, you're bloody well right [oops:
digression]).  To put it more succinctly, you cannot do this with some
sort of pseudo tty support (I _know_ I've tried).  The problem is that
a lot of programs try to be (too?) smart about their environment and
what they do is call isatty(3) which returns false if its' arg is not
a file descriptor connected to a tty.  [I learned this after writing
a history filter for xlisp: it worked fine until I tried to call vi]

Now, there is a way around this problem:  It's a kludge, and
depends on you using shared libs (like on the pc7300), but it's worth
mentioning:

Snag the source to isatty (or rewrite it) and have it return true for
file descriptors that are pipes.  Reinstall the function in the shared
lib, reboot and away you go.  Stuff like "vi foo | wc" will be
mishandled, but who does that anyway?  :-)

Yeah, well, you asked, ok?

BTW - SysV.3 *has* pttys - they're called sxt's (I think).  Someone
will jump on this if I'm wrong....
-- 
Larry McVoy 	        mcvoy@rsch.wisc.edu  or  uwvax!mcvoy

"It's a joke, son! I say, I say, a Joke!!"  --Foghorn Leghorn