Path: utzoo!censor!geac!torsqnt!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!newstop!texsun!convex!convex.com!tchrist
From: tchrist@convex.com (Tom Christiansen)
Newsgroups: comp.lang.perl
Subject: fun with scoping
Message-ID: <111557@convex.convex.com>
Date: 17 Dec 90 04:28:35 GMT
Sender: news@convex.com
Reply-To: tchrist@convex.com (Tom Christiansen)
Organization: Convex Computer Corp, Richardson, TX
Lines: 33

Once upon a time I had an annoying problem: I diff the run of a nightly
find to discover changes to setid files and devices.  Now, I happen to have
several accounts, like uucp and notes, that have files of this sort and
with more than one login to each uid, so every time the passwd and group
files hash (YP), I pull out a different id and so get reams of nightly
output.  This annoyed me.  So I wrote the following filter to convert
everything out of 'find -ls' back into numbers so it would stop changing:

    #!/usr/bin/perl
    $fmt = 'a22 A9 A8 a*';
    while (<>) {
	($pre, $login, $group, $post) = unpack($fmt, $_);
	print pack($fmt, $pre, &get(*login), &get(*group), $post);
    }
    sub get {
	local(*id) = @_;
	$id{$id} = $id =~ /^\d+$/ ? $id : &id       unless defined $id{$id};
	$id{$id};

    }
    sub login { (getpwnam($id))[2]; }
    sub group { (getgrnam($id))[2]; }


I would say that this is an interesting program, eh?  :-)   If this isn't
a great demo of Perl's um, unique, scoping behavior, I don't know what is.
If you think that's scary, note that if we s/get/id/g the program still works!

--tom
--
Tom Christiansen		tchrist@convex.com	convex!tchrist
"With a kernel dive, all things are possible, but it sure makes it hard
 to look at yourself in the mirror the next morning."  -me