Your image tag is pointing to the actual path to the file on the server, instead of the path relative to the webroot? Try change it to point to /cgi-bin/remote_address.pl instead and see if that helps.

• My web server is set up to execute files that have a .cgi extension as CGI scripts. Only. Your web server my be set up the same way. Try changing the name of your CGI script to remote_address.cgi
• Your CGI script should always print a Content Header. Even though you don't "have to" in this case, know that everytime the script is execute an error is being generated in the error log.
• Opening a file in append mode will create the file if it doesn't exist. You can trim your 12 lines of code down to 3. Also, be sure that the file has the proper permissions or the web server will not be able to write to it. I recommend touching the file ip.log in the directory of choice, su'ing to root, chown the group to the web server, and then chmod the file to 664. If you don't have root access, you can't chown the file and you will have to chmod it 646 or 666.

use strict;
use warnings;
use CGI qw(header);

my $file = '/full/file/path/to/ip.log';
open LOG, '>>', $file or die "can't open ip log: $!\n";
print LOG "$ENV{REMOTE_ADDR}\n";

print header('image/png');
[download]

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)

There are a coupld of issues with this script that you could improve:

• You may need to set the PATH environment variable, or have the full path you your 'touch' and 'chmod' programs (or better yet, let 'open' create the file for you, and why not use the built in perl version of 'chmod').
• Check to make sure that the webserver can actually write to the directory that you have listed. Remember that the web server may run as a different user than what you normally use.
• You are not locking the file when you are writing to it. If you have two requests to this script concurently you could mess up the file.
• You are not returning anything to the browser. You need to return an image of some sort, and a full set of headers.

Here is your script with file locks. It always returns a clear gif to the browser even if the open failed.

#!/usr/bin/perl

use Fcntl ':flock';
use MIME::Base64;
use CGI qw(header);

my $file = "/home/master/webroot/perlskripts/ip.log";

if ( open(my $fh, '>>', $file) ) {
  # lock the file
  flock($fh,LOCK_EX);

  # seek to the end in case someone altered 
  # the file since we opened it
  seek($fh, 0, 2);

  # add the entry to the file
  print $fh "User from ".$ENV{'REMOTE_ADDR'}." logged on\n";

  # unlock
  flock($fh,LOCK_UN);
} else {
  print STDERR "Could not open file for append: $!\n";
}

# always send a clear gif to the browser
my $q = CGI->new();
$q->header(-type => 'image/gif');

# The following is a base64 encoded 1x1 clear gif image
print MIME::Base64::decode_base64('R0lGODlhAQABAIAAAP///wAAACH5BAEAAAA
+ALAAAAAABAAEAAAICRAEAOw==');
[download]

- Cees

<img src="/var/www/cgi-bin/remote_address.pl" height="0" width="0" alt="script">

Just a quick shot in the dark: are you sure you want "/var/www/cgi-bin/remote_address.pl" and not something more like "/cgi-bin/remote_address.pl"?

Update: While you are developing the code you might want to work with a larger, visible image so that you can see whether script has run correctly.

You should be aware that some privacy tools remove 1x1 pixel images loaded from third party sites on the grounds that loading the image can be used for tracking the user without their consent.