You can use PHP to detect crawling activity, rotate images/banners, and process forms. Here is an example of code that will email you whenever Google crawler Googlebot visits your page by detecting the useragent. You could expand the code to include other crawlers, add date and time stamp, and validate the IP to exclude impostors. I left that stuff out for simplicity and because you can  get that info from your webstats/logs. Just copy and paste this code in your web page to try it out. Note that the page may have to end with .php file extension to work, it depends on how your web server is setup.

<?
if(eregi(“Googlebot”,$_SERVER['HTTP_USER_AGENT'])){

//put your email address below
$address=youname@yourdomain.com;
$subject=”Google visited “.$_SERVER[’HTTP_HOST’];
$message=”Googlebot visited today.”;
mail($address, $subject, $message);
}
?>

Here is an example of how to display  random images in a web page, it will pick one of the three banners each time the page loads. You could easily add more cases here or change the img src line to make this a random text function.

<?
$randomimage = Rand (1,3) ;

//put your image name at bannerx
switch ($randomimage)
{
case 1:
“banner1″;
break;

case 2:
“banner2″;
break;

case 3:
“banner3″;
break;
}

echo ‘<img src=”‘$randomimage.’” border=0>’;

?>

Another cool thing you can do is filter form data to by blocking bad words, banning ip addresses, and setting a timer with a cookie. There is nothing worse than having your website form spammed. You can get the visitor’s IP address with a built in php function and then check it against a list of bad IP addresses you have stored in a list called an array. You can modify this to include words by replacing the IP addresses with words. This is useful if there is a relatively small number of abusers. In the case of larger numbers, blocking at the server level using iptables or a firewall may work better for you.

Here is the code for blocking IPs and you can add more IPs to the array if needed:

<?
$banned_ip_addresses = array(’4.2.5.5′, ’64.43.67.19′, ’207.22.32.152′);

if(in_array($_SERVER['REMOTE_ADDR'], $banned_ip_addresses))
{
echo “You are banned.”;
} else {
continue with form processing…
}

If you are having problems with abusive surfers filling out your forms with constantly changing ip addresses, you can stop them by adding a cookie. A cookie is a small piece of code sent to the user’s pc to identify them.  Note that not all browsers will accept cookies, but most will. Once the cookie is set, you check for the existence of it in your form processing. Here is an example:

//this sets time to 7200 seconds, 2 hours
<?
setcookie(“userx”, “cookie1″, time()+7200);
?>

Then add the code below to find out if this person has been on your page before:

<?
if (isset($_COOKIE1["userx"])){
echo “You have already filled out this form recently”;

} else {
continue with form processing…
}
?>

There is a plethora of PHP support websites on the Internet. My longtime favorite is  PHP Freaks Forum where you can post  technical questions and read responses. Another good one is the Digital Point PHP Forum. If you are looking for scripts then visit Hotscripts, where you will find many, some free and some paid. Also check out Free Scripts Directory,  Script Repository, and PHP Resource Index. They have scripts for: counters, auctions, voting, calculators, searching, support ticketing, etc.

PHP works fine on both Linux and Windows systems. If you have a Linux box then chances are good that it is already installed; if not, visit php.net to download it. PHP is not standard on Windows but it can be installed. If you need technical support we can help you with installing or upgrading.

PHP is very powerful. In an upcoming post I will explain how to speed it up using accelerators, pull data from a database, write it to a webpage, and add functionality using extensions.

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Here are a few more one-liners. I also call for the assistance of our audience; if anyone has more reliable or efficient methods to accomplish the ends in this article, get involved and comment!

1. Obtain your internet IP
   There are two ways to do this (both below.) This can be useful in bash scripts that require your IP address. It’s useful in a dynamic IP environment when handling dynamic DNS in some fashion; though can be useful in a variety of scripts in which NAT may exist making eth0 unreliable for this information.
   shell# wget -O – -q checkip.dyndns.org | grep -o “[[:digit:].]+”

   You can also use curl if it’s your tool-of-choice.

   shell# curl -s http://checkip.dydns.org/ | grep -o “[[:digit:].]+”

   If you’ve got a static IP that is directly connected to the internet; it’s best to just scrape the information out of ifconfig.

   shell# /sbin/ifconfig eth0 | grep inet | grep -o “[[:digit:].]+” | head -n 1
2. Get Distribution Information/Version
   From time to time we get support tickets or calls asking “What distribution of Linux am I running?”. Here’s a way to ascertain this under most modern Linux distributions we offer.

   Most Linux distributions follow the “Linux Standard Base” and have a file in /etc matching *release. You can take a look by running:

   shell# cat /etc/*release

   This does the same thing if you find it easier to remember.

   shell# lsb_release –all

   NOTE: You may have to cat the file /etc/debian_version on some Debian releases.

3. Shortcut to list all system users
   I stumbled upon this one by a typo once where you can get a peek of system users. This shouldn’t be considered authoritative, as /etc/passwd is your daddy; but it’s quick to verify the spelling of that strange developer who insists on the username supercalifragilistic_expialidocious.
   Tested on: Debian, Redhat
   shell# ~(HIT TAB TWICE HERE)
4. Lost Plesk Password
   Here’s one of those gems that we keep close to our chest, but I’m willing to reveal it to you. If you misplace your Plesk Admin password, on UNIX it stores it in /etc/psa/.psa.shadow. This is a read-only file, changing the password here does not change it for Plesk. It’s a good way to jot your memory if you forget though.
   shell# cat /etc/psa/.psa.shadow

Continue to keep an eye out for my next list!

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• Workstation Backup Solutions Pt. 3: Redundancy
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I thought I’d share some intriguing and useful one-liners that could make your life easier on the Linux/Unix shell environment. I hope to offer a regular multi-part series for those who are fans of the Linux platform.

1. View Physical Console via SSH
   This will view the console (and makes assumption that the console is an 80 character screen.) It’s helpful to scrape error messages that are printed to the local console. Great for when you don’t have physical access to the server and need to see the terminal; we also find it useful here by eliminating unnecessary trips to the data center floor.

   shell# sudo cat /dev/vcs1 | fold -w 80

2. Remove multiple RPM packages by a defined pattern
   This is useful for remove all packages that are part of a common suite. This example would uninstall any package in the system with ‘php’ in the name. (Disclaimer: Check what packages contain the string prior to running this. Unpredictable results could remove system critical packages! I’d suggest this for advanced shell users only.)

   shell# yum erase `yum list installed | grep ‘php’`

3. Reduce a file to zero bytes
   I’m sure every administrator has needed to zero out a log file taking too much space; or clear a users mail spool. Many commands involve piping /dev/null to the file or similar. The following command is probably the easiest and quickest way that many users overlook.

   shell# > file_to_wipe.txt

4. Look at the strings stored in RAM
   This one is more for fun; though it could be used for security auditing. This command will access the system RAM and reveal text strings stored in memory. Don’t worry, this file is read-only by the kernel. You can usually find interesting data stored in memory with this command.

   shell# sudo dd if=/dev/mem | cat | strings

That’s it for now; more in this series coming soon.

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• PHP Script Tips and Resources
• Drupal – Free Website Building Tool
• Workstation Backup Solutions Pt. 3: Redundancy
• Workstation Backup Solutions Pt. 2: Methods & Retention
• Send Us Your Postcards!
• Workstation Backup Solutions Pt. 1: Having One
• Employee Appreciation and the Lost Art of the Road Trip
• A Resolution to Keep Resolutions
• Happy Holidays!