The bug in the module is that it is not prepared to handle a sort routine that can receive 2 distinct arguments and return 0. If you enable a last comparison in your sort routine that just does $Sort::External::a cmp $Sort::External::b then you won't get an endless loop. Alternately, assuming that Perl is using a stable sort (it does by default I believe, but that's not a safe default) you can fix the bug with the following patch to Sort/External.pm: 
--- External.pm.bak    2008-07-11 22:30:52.000000000 -0700
+++ External.pm    2008-07-11 22:52:14.000000000 -0700
@@ -322,7 +322,7 @@
             $comparecode = sub {
                 my $test = shift;
                 return 0 if $test eq $cutoff;
-                my $winner = ( sort $sortsub( $cutoff, $test ) )[0];
+                my $winner = ( sort $sortsub( $test, $cutoff ) )[0];
                 return $winner eq $cutoff ? 1 : -1;
             };
         }

[download]
While I'm at it I should mention that you have a lot of unnecessary checks in your comparison. You're writing 
     # ....
     return -1 if $hours1 < $hours2;
     return 1 if $hours1 > $hours2;
     return -1 if $hours1 == $hours2 && $minutes1 < $minutes2;
     return 1 if $hours1 == $hours2 && $minutes1 > $minutes2;
     return -1 if $hours1 == $hours2 && $minutes1 == $minutes2 && $sec
+onds1 < $seconds2;
     return 1 if $hours1 == $hours2 && $minutes1 == $minutes2 && $seco
+nds1 > $seconds2;

[download]
but if $hours1 and $hours2 are different then you'll never get to the minutes comparison. So you can get rid of those and just have: 
     # ...
     return -1 if $hours1 < $hours2;
     return 1 if $hours1 > $hours2;
     return -1 if $minutes1 < $minutes2;
     return 1 if $minutes1 > $minutes2;
     return -1 if $seconds1 < $seconds2;
     return 1 if $seconds1 > $seconds2;

[download]
But you can write this more idiomatically using the fact that || short circuits: 
     return $hours1 <=> $hours2
         || $minutes1 <=> $minutes2
         || $seconds1 <=> $seconds2
         || $Sort::External::a cmp $Sort::External::b;

[download]
Incidentally in one of the few useful uses of prototypes in Perl, if a sort sub has a prototype of ($$) then the arguments are passed in as @_ and not $a, $b. So if you write 
my $sortscheme = sub ($$) {
    my @fieldsa = split(" ", shift);
    my @fieldsb = split(" ", shift);
    # ...
};

[download]
then you don't have to worry about what package the sort is coming from.

Oh and a final tip? You should use strict.pm. Always.

In reply to Re: Problem with Sort::External 0.16 by tilly
in thread Problem with Sort::External 0.16 by Anonymous Monk

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