The trivial sort operation looks like this:

for (sort {
  (my $l = $a) =~ /fwlog\.(\d+)/;
  (my $r = $b) =~ /fwlog\.(\d+)/;
  $l <=> $r;
} @files) {
  print "$_\n";
}
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Trivial in terms of straight-forward thought and coding time. But that's rather inefficient in CPU time. Better is:

for (map {
  $_->[1]
} sort {
  $a->[0] <=> $b->[0]
} map {
  /fwlog\.(\d+)/;
  [ $1, $_ ]
} @files) {
  print "$_\n";
}
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The key here is to read it backwards. You have @files. You create a mapping of those @files to anonymous arrays where the first element in the array is the number you're sorting on, and the second is the whole filename you started with. You then sort this list of anonymous arrays, comparing on the first element in the array. You then use map to pull out the original filename in the order that sort created. It's a bit convoluted, but once you get your head around it, you'll be impressed by the sheer elegance. I know I was :-)

Update: Thanks to bmann on catching the typo in the sort - had a 1 where I should have had a 0.