#!/usr/local/bin/perl 
# Randomly picks a filename from $DIRSPEC and redirects the browser to it.
# It sets the Expiration header so that the contents will have to be
# retrived every time the user returns to the page or uses the Reload
# button.

# 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!.*/!!;

# set the header & redirect user to the new location
print "Location: $URL/".urlencode($file)."\n";
print "Date: ".httpdate(time)."\n";
print "Expires: ".httpdate(time)."\n";
print "Pragma: no-cache\n\n";

# that's all
exit(0);

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

# Returns date & time string for use in HTTP headers:
# Format: Sun, 15 Mar 1998 22:02:28 GMT
sub httpdate {
    my($d)=shift;
    my(@l)=split(/\s/,scalar gmtime($d));
    # change: Sun Mar 15 14:03:04 1998
    #   into: Sun, 15 Mar 1998 14:03:04 GMT
    return("$l[0], $l[2] $l[1] $l[4] $l[3] GMT");
}