It is sometimes necessary to block people from using your site, dependent on their IP address. A users IP address can be detected by PHP using the $_SERVER superglobal and the parameter REMOTE_ADDR.

The code includes two ways to load the list of IP addresses. The first is by hard coding it into an array, and the second is by the use of a plain text file called "blocked_ips.txt". The format of this file is simply a list of IP addresses, with one address on each line. Through the use of the file() function this file is loaded as an array into of addresses.

To stop access to a directory (and anything in that directory) all you need is a simple RewriteRule.

RewriteEngine on
RewriteBase /
RewriteRule ^exampledirectory/(.*)$ / [R=301,L]

In this example, if this .htaccess file resides in the root directory of the site and you try to access anything within /exampledirectory you will be redirected back to the root folder. To redirect to another folder (like anotherdirectory) on your web server use the following rule.

RewriteEngine on
RewriteBase /
RewriteRule ^exampledirectory/(.*)$ /anotherdirectory [R=301,L]

The following function will reduce a hexadecimal colour string by a set value. It can take three and six digit colour values.

function ColorDarken($color, $dif=20)
{
 $color = str_replace('#','', $color);
 $rgb = '';
 if (strlen($color) != 6) {
  // reduce the default amount a little
  $dif = ($dif==20)?$dif/10:$dif;
  for ($x = 0; $x < 3; $x++) {
   $c = hexdec(substr($color,(1*$x),1)) - $dif;
   $c = ($c < 0) ? 0 : dechex($c);
   $rgb .= $c;
  }
 } else {
  for ($x = 0; $x < 3; $x++) {
   $c = hexdec(substr($color, (2*$x),2)) - $dif;
   $c = ($c < 0) ? 0 : dechex($c);
   $rgb .= (strlen($c) < 2) ? '0'.$c : $c;
  }
 }
 return '#'.$rgb;
}

Here are some examples of use.

echo ColorDarken('#123456'); // #002042
echo ColorDarken('#666'); // #444
echo ColorDarken('#ffffff'); // #ebebeb
echo ColorDarken('#ffffff',1); // #eeeeee

Splitting an array into sections might be useful for setting up a calendar or pagination on a site. Either way there are numerous ways to do this but the following seems to be the quickest and most reliable method.

function sectionArray($array, $step)
{
 $sectioned = array();
 
 $k = 0;
 for ( $i=0;$i < count($array); $i++ ) {
  if ( !($i % $step) ) {
   $k++;
  }
  $sectioned[$k][] = $array[$i];
 }
 return $sectioned;
}

Run the function by passing it an array, in this case I am going to split the alphabet into 5 arrays of 5 letters.

$array = range('a','z'); // create an array from a to z
 
echo '<pre>'.print_r(ArraySplitIntoParts_Shorter($array,5),true).'</pre>';

This produces the following output.

A whois query will tell you some information about a domain name. Although not available as a default on Windows systems you can type:

whois google.com

On most Linux installs and see some information about the google.com domain. What information you see depends on the domain you are looking at and the rules that the Top Level Domain (TLD) employs. For more information on whois you can take a look at the Wikipedia entry on the subject.

In order to get this information in PHP you will need to ask the appropriate TLD whois server for information about the domain. But where do you get a list of the servers? Well the root zone database has a comprehensive list of domains, and by clicking on the TLD links you can see whois information at the bottom of the page.

Having a header file that prints out a standard menu on a site is a good idea and saves you time in the long run as you only have to edit one file to change an item on the menu. However, what if you only want to display a menu or sub-menu when a particular page is loaded? This is a common problem, and finding out what page you are on is something that all PHP programmer come across at some point or another.

The PHP $_SERVER superglobal array has three items of interest which can be used to find out the current page. These are PHP_SELF,REQUEST_URI and SCRIPT_NAME and they all appear to have the same values but there are some subtle and important differences. Here are some examples of their values (on the right) with the original URL (on the left).

PHP_SELF

Rot13 (which stands for "rotate by 13 places") is a name given to a simple encoding algorithm (or substitution cipher) that is used to mask text. It works by making each letter 13 spaces further along in the alphabet so that a becomes n and b becomes o. For the letter n the alphabet starts again from the beginning.

The cipher can be used both ways so that any string encoded with the function can then be easily decoded with the same function. For this reason it is a very poor mechanism of encoding, but can be used if you want to mask some text but are not concerned about people reading it. It is commonly used on forums in order to hide spoilers and solutions from readers who don't want to see them.

Here is the function.

If you allow users to upload data to your site you might have a situation where a data directory might be full of temporary files. In the long term you will want to get rid of these files as they have served their purpose and are no longer needed.

Here is a function that can be used to delete any files in a directory that were created more than 20 minutes ago. It uses the glob() function to find all files of a particular type and then uses the filectime() function to figure out when the file was last modified (or created). It will then delete (unlink) any files that were created more than 20 minutes ago.

Lewis Carroll devised a mechanism to work out the day of the week given a particular date and was published in Science in 1887. Here is a PHP function that works out the day of the week given the date that uses the same mechanism that Lewis Carroll devised. The mechanism isn't very complicated, but rather than explain it twice I have just put a lot of comments in the code to indicate what is happening.