According to an earlier post, the bold fields are the ones you're sorting on. If that's truly the case, and if the text within brackets comes from a limited dictionary, then this sort can be done entirely with numbers.

First, combine the CD number with the file number, yielding (in this case)   101100809 Then map "Account Number" into its pre-determined sequence number. You're then left sorting something like   [ 101100809, 47, seek-address ] on the first two fields, which are now numbers.

How about extending it to something like

pack("n N n", $1, $2, $3).$4

thereby we would sort CD# > 9 correctly, decrease the memory footprint and allow for the fast intrinsic ASCIIbetical sort.
Perhaps even to the point where fast hash lookups can be used.

It's a pity the data is in practice unavailable

Here's what I would like to time ...


.
.
my (%sort_hash);
my $offset = 0;
while (<IN>) {
    if(  m/^CD(\d+)\\(\d+)\.pdf\((\d+)\)\s-\s\[(.+?)\]/  ) {
        $sort_hash{pack("n N n", $1, $2, $3).$4} = $offset;
    } 
    $offset = tell(IN);
}

foreach my $k (sort keys %sort_hash) {
   seek IN, $sort_hash{$k}, 0;
   print OUT scalar(<IN>);
}
[download]

And then, why not pack the offset on the end, and unpack substr -4 when you're done. Then you're down to a simple array sort and the only problem is the original one: sooner or later you scale up till you're paging forever.

  p