If you've got it to work by now, may I point out a couple of possible problems (if you deliberately glided over these issues in the interests of simplicity, I apologise in advance :).

(NB: I assume, for the sake of argument, that you are prompting a user to enter (a full filepath to) a directory, and then letting them do something with this directory unless it is on the 'banned' list.)

1. Windoze filenames are case-INsensitive. So as well as banning 'd:/perl' you need to ban 'D:/Perl', etc. This is of course easy to solve.

2. You generally need to check for the user entering 'd:/perl/' and 'd:/perl\' (or 'd:perl\\' etc) as well as 'd:/perl'. This is easy to solve too.

3. If there is any chance of you needing to ban the current directory (where the code is being executed) and/or its parent, you should check for the user entering '.' or '..' (best, probably, to put them in your 'banned' list).

4. Concerning the following lines of your code:

$folder =~ /^($bannedF[$_]).*/;
return BANNED if ($1);
[download]

I'm not sure what it does. If it is simplified to:

the problem becomes more apparent, namely that if you ban for example 'c:/win', you are also banning folders such as 'c:/wings', 'c:/winter_weather' etc. One way to solve this would be to ban anything that starts with 'c:/win/' (having stripped out spurious trailing slashes as under point 2 above).

There are no doubt other 'security' problems than those listed above, and more checking of user input is certainly required. However, this is how I'd do it if security weren't a vital issue:

use strict;
use warnings;

# Global variables:
use vars qw ( @BANNED $INC_SUBDIRS );
@BANNED = qw ( .
               ..
               c:/perl/progs
               c:/winnt/system32
               d:
              );
$INC_SUBDIRS = 1; # change to 0 or '' to turn off

print "Enter a full pathname: ";
chomp ( my $dir = <> );

# Remove trailing slashes:
$dir =~ s{[/\\]+$}{}g;          ;
print "Verboten!" and exit if is_banned( $dir );

# Just for testing:
opendir DIR, $dir or die "can't opendir $dir: $!";
print "$_\n" for readdir DIR;
closedir DIR;

sub is_banned {
   my $folder = lc shift; # lc for lower case
   for ( @BANNED ) {
      return 1 if $folder eq $_;
      if ( $INC_SUBDIRS ) {
          return 1 if $folder =~ /^$_\//;
      }
   }
}
[download]

hth

dave