my @files = <DATA>; chomp @files;

@files =
      map { substr $_, 10 }
      sort
      map { sprintf "%10s%s", /(\d+\w{3}\d{4})/, $_ }
      @files;

print join "\n", @files, '';

__DATA__
fwlog.14Mar2005.gz
fwlog.15Mar2005.gz
fwlog.16Mar2005.gz
fwlog.1Mar2005.gz
fwlog.2Mar2005.gz
fwlog.20Mar2005.gz

##</code><code>##

my @months = qw( Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec );
my %months;

my $i = 1;
$months{$_} = sprintf( "%02d", $i++ ) for @months;

print $_, "\n" for map { $_->[0] } 
sort { 
  $a->[1] <=> $b->[1] or 
  $a->[2] <=> $b->[2] or 
  $a->[3] <=> $b->[3] 
} 
map { 
 (split(/\./,$_,3))[1] =~ /^(\d+)([A-Za-z]+)(\d+)$/; 
 [$_, $3, $months{$2}, sprintf("%02d", $1) ] 
} @files;