@files = sort { my ($ad) = ( $a =~ /fwlog\.(\d+)\w+/ ); 
                my ($bd) = ( $b =~ /fwlog\.(\d+)\w+/ ); 
                $ad <=> $bd } @files;

print join "\n", @files;


OUTPUT:
fwlog.1Mar2005.gz
fwlog.2Mar2005.gz
fwlog.3Mar2005.gz
fwlog.4Mar2005.gz
fwlog.5Mar2005.gz
fwlog.6Mar2005.gz
fwlog.7Mar2005.gz
fwlog.8Mar2005.gz
fwlog.9Mar2005.gz
fwlog.14Mar2005.gz
fwlog.15Mar2005.gz
fwlog.16Mar2005.gz
fwlog.17Mar2005.gz
fwlog.18Mar2005.gz
fwlog.19Mar2005.gz
fwlog.20Mar2005.gz
fwlog.21Mar2005.gz