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From: mdb@ESD.3Com.COM (Mark D. Baushke)
Newsgroups: comp.lang.perl
Subject: Re: Cute hack around tiny bug (Re: Help a perl apprentice)
Message-ID: <MDB.90Oct28220540@kosciusko.ESD.3Com.COM>
Date: 29 Oct 90 06:05:40 GMT
References: <18840001@hp-lsd.COS.HP.COM> <21380@orstcs.CS.ORST.EDU>
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In-reply-to: pvo@sapphire.OCE.ORST.EDU's message of 28 Oct 90 04:36:52 GMT

On 28 Oct 90 04:36:52 GMT, pvo@sapphire.OCE.ORST.EDU (Paul O'Neill) said:

Paul> I really like Tim Chambers' df massager and Larry's rewrite of it.
Paul> -------------
Paul> #!/usr/local/bin/perl

Paul> open (BDF_PIPE, "bdf @ARGV |");

Paul> print <<End;
Paul> Filesystem                     Free (Mb) %Used
Paul> ==============================|=========|=====
Paul> End

Paul> while (<BDF_PIPE>) {
Paul>     ($fs, $kbytes, $used, $avail, $capacity, $dirname) = split;
Paul>     next unless $kbytes > 0;
Paul>     # next unless $fs;          # uncomment to delete nfs filesystems
Paul>     $line{$avail} = sprintf("%30.30s%10.1f%6s\n",
Paul>                         $dirname . '.' x 30,
Paul>                         $avail / 1000, $capacity);
Paul> }

Paul> sub revnum { $b <=> $a; }

Paul> foreach $key (sort revnum keys(%line)) {
Paul>     print $line{$key};
Paul> }

Paul> print "\n";
Paul> ----------------------

Paul> There's a tiny bug in there, though.

Paul> What if 2 file systems have the same available space? (ie. zero :-)

Paul> The old $line{$avail} gets wiped by the new $line{$avail} and is not
Paul> reported.

I sent Larry private e-mail about this and suggested a one character
change to the script change 

     $line{$avail} = sprintf("%30.30s%10.1f%6s\n", ...);
to
     $line{$avail} .= sprintf("%30.30s%10.1f%6s\n", ...);

This works fine if you don't care about the order of two entries with
the same amount of available space.

Larry agreed and then suggested that another way to get around it
would be to use

     $line{$avail.'.'.$seq++} = sprintf("%30.30s%10.1f%6s\n", ...);

Paul> It occured to me that a good way to handle this was to add a
Paul> small number, say 0.1, to $avail if $line{$avail} aready
Paul> existed.  But what if there were *three* (or more) file systems
Paul> with the exact same available space?

Using a linearly increasing sequence number is probably a better
solution in this case. Even using rand() there is no guarentee that
you will not arrive at duplicate keys.

Enjoy!
-- 
Mark D. Baushke
mdb@ESD.3Com.COM