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From: marcp@beryl.berkeley.edu.UUCP
Newsgroups: comp.unix.questions
Subject: A couple questions
Message-ID: <3164@jade.BERKELEY.EDU>
Date: Tue, 14-Apr-87 03:13:42 EST
Article-I.D.: jade.3164
Posted: Tue Apr 14 03:13:42 1987
Date-Received: Wed, 15-Apr-87 05:18:36 EST
Sender: usenet@jade.BERKELEY.EDU
Reply-To: marcp@beryl.berkeley.edu (Marc M. Pack)
Organization: University of California, Berkeley
Lines: 24

Hello!  I've a couple of questions in UNIX 4.2.

1.  How do programs like "more" distinguish between text files and
	executable files?  Hopefully, there's something surer than
	just taking a sample of a file and testing it.  (This question
	came up when a bunch of people started accidentally sending
	executables to a line printer, and I was trying to figure
	out a way to filter out the execs from the texts).

2.  Is it possible to, while in a C program, call another program and
	put it into the background?  Actually, I know it's possible,
	'cause I can do it with a line like:

		system("cat textfile &");

	This won't work, however, if I try to "more" the file instead.
	What determines what can be put in the background and what can't?
	Is there some way to run a program from within a program, and have
 	it return upon completion to the original program besides "system"?
	(The execl series, of course, doesn't return.)

Thanks for your time,

							Marc M. Pack