my $dir   = '/a/b/c'; 
my @files = (); 
 
opendir DIR, $dir or die "Can't open dir $dir : $!"; 
@files = grep { !/^\./ } readdir(DIR); 
closedir DIR; 
 
open  FILE, $files[rand @files] or die "Can't read file: $!"; 
read  FILE, my $string, -s FILE; 
close FILE; 
 
print "Content-type: text/html\n\n"; 
print $string;

my $headers = { 
       'gif' => 'image/gif', 
       'html => 'text/html', 
       'txt' => 'text/plain' 
       etc.... 
}; 
 
my ($rand, $ext) = $files[rand @files] =~ /^([^.]+\.([^.]+))$/; 
 
open bla bla 
 
print "Content-type: $headers->{$ext}\n\n"; 
print $string;