my $url = "http://www.site.com/subdomain/a9934aa.html";

// prints all the numbers only in the filename part
my @buffer = split(/\//,$url);
my $buffervalue = pop(@buffer);
$buffervalue =~s/[^\d]//g;
print $buffervalue; 

// for numbers in entire url
my $buffer = $url;
$buffer =~s/[^\d]//g;
print $buffer;