#!/usr/local/bin/perl 
# Randomly picks a filename from $DIRSPEC and returns it
# It doesn't set the Expiration: header, so most web browsers will
# probably not actually run this script more than once.
#

# where to search for the files
$DIRSPEC="/home/httpd/html/web/*.{gif,jpeg,jpg}";

# URL where where the files are served from
# example: http://yoursite.com/dirname
$URL="/web";

# get a list of all the files
@list=glob($DIRSPEC);

# pick a random file name from the list
$file=$list[ (time&0xffff ^ $$) % ($#list+1) ];

# remove path from the name
$file=~s!.*/!!;

# redirect user to the new location
print "Location: $URL/".urlencode($file)."\n\n";

# that's all
exit(0);

# encodes a string, encoding non-alphanumerics into %xx codes
sub urlencode {
  my($s)=shift;
  $s=~s!([^a-z0-9\.\-])!sprintf("%%%02x",ord($1))!ige;
  return $s;
}