Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!sdd.hp.com!elroy.jpl.nasa.gov!jpl-devvax!lwall
From: lwall@jpl-devvax.JPL.NASA.GOV (Larry Wall)
Newsgroups: comp.lang.perl
Subject: Re: Questions about exec and scripts called from cron
Message-ID: <9733@jpl-devvax.JPL.NASA.GOV>
Date: 28 Sep 90 21:38:55 GMT
References: <1180002@hpcc01.HP.COM>
Reply-To: lwall@jpl-devvax.JPL.NASA.GOV (Larry Wall)
Organization: Jet Propulsion Laboratory, Pasadena, CA
Lines: 39

In article <1180002@hpcc01.HP.COM> okamoto@hpcc01.HP.COM (Jeff Okamoto) writes:
: Two more puzzling questions for patchlevel 18:
: 
: 1. Why does this construct not do what I think it should?
: 
: 	exec "/non-existent-file" || die "Can't exec: $!\n";

Because exec is a list operator, and thus has a lower precedence than ||.
Say this:

	exec("/non-existent-file") || die "Can't exec: $!\n";

or

	exec "/non-existent-file";
	die "Can't exec: $!\n";

: 2. Why does this construct not work when this script is called
:    from cron?
: 
: 	#!/usr/local/bin/perl
: 	eval "exec /usr/local/bin/perl -S $0 $*"
: 		if $running_under_some_shell;

I don't have enough to go on here, but bear in mind a coupla three things.
First, cron runs without much of a PATH, and the -S switch above
uses PATH to try to locate the script.  Second, cron could conceivably
be feeding the text above to /bin/sh through stdin, in which case $0 isn't
going to be meaningful, and you'd probably try to execute the first argument
of $*.  Third, if the arguments you're passing contain any whitespace,
you should instead use

	eval 'exec /usr/local/bin/perl -S $0 "${1+$@}"'
		if $running_under_some_shell;

Hope that helps.  You might just invoke perl directly from cron instead
of relying on the eval-exec hack.

Larry