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From: lwall@jpl-devvax.JPL.NASA.GOV (Larry Wall)
Newsgroups: comp.lang.perl
Subject: Re: Need $? for open()
Keywords: new feature request
Message-ID: <7605@jpl-devvax.JPL.NASA.GOV>
Date: 29 Mar 90 22:49:28 GMT
References: <23449@pasteur.Berkeley.EDU> <100906@convex.convex.com>
Reply-To: lwall@jpl-devvax.JPL.NASA.GOV (Larry Wall)
Organization: Jet Propulsion Laboratory, Pasadena, CA
Lines: 44

In article <100906@convex.convex.com> tchrist@convex.COM (Tom Christiansen) writes:
:     It's known that opening pipes to non-existent programs doesn't 
:     usually trigger useful error diagnostics.  In particular, while
:     writing on a badly-opened output pipe will (eventually) trigger a
:     SIGPIPE (which you can look for), reading from a badly-opened input 
:     pipe just gets you EOF.
: 
:     A possible work-around for the bad input pipe follows:
: 
: 	$kid = open (PIPE, "bogus_command |");  # really should check $kid != 0
: 	(kill 0, $kid) || die "bogus_command failed";
: 
: 
:     This works fine if bogus_command doesn't have shell metas in it, but
:     if it does, the shell may well not have exited before the kill 0.
: 
:     You can introduce a delay,
: 
: 	$kid = open (PIPE, "bogus_command </dev/null |");
: 	sleep 1;
: 	(kill 0, $kid) || die "bogus_command failed";
: 
:     but this is sometimes undesirable and in any event does not guarantee
:     correct behavior.  But it seems slightly than nothing.  

If you want to get a SIGPIPE on a bad input command, you can do it like
this if you don't have shell metacharacters, or if the supposed metacharacters
really aren't.

	$kid = open(PIPE, "-|");
	die "Couldn't fork" unless defined $kid;
	if (!$kid) {	# we don't have kid, so we are one
	    exec "this", "is", "a", "bogus", "command";
	    kill 'PIPE', getppid;
	    exit 1;
	}

	while (<PIPE>) { ...

If you do want the shell to run, then you can probably do something like

	open(PIPE, "bogus command || kill -PIPE $$ |")

Larry