This page is a collection of simple replacement rules you can use for yourself. Before you can use any of this, you should have a filter as a container.

Simple replace (case sensitive)

This will convert all occurrence of foo into bar, but it is case-sensitive, means that it won't work for Foo, or fOO.

• Pattern: /foo/
• PHP Code: off
• Replacement: bar

Simple replace (case insensitive)

This will convert all occurrence of foo into bar, and it is not case-sensitive, means that it will work for Foo, and fOO.

• Pattern: /foo/i
• PHP Code: off
• Replacement: bar

Tag replacer

This will convert all occurrence of <hello> into Hello World. It is not case sensitive, and it can handle spaces within tag, like < hello >, by using \s* pattern. That pattern means "zero, or more spaces here".

• Pattern: /<\s*hello\s*>/i
• PHP Code: off
• Replacement: <strong>Hello World!</strong>

Links

Adds link to drupal.org on the occurrence of <drupal/>. Notice that there is no \s* pattern, so it is not intended to replace < drupal />. You should enter exactly <drupal/>. And notice that backslash (\/), because slash (/) has a special meaning in regular expressions, so we must escape it using backslash.

• Pattern: /<drupal\/>/i
• PHP Code: off
• Replacement: <a href="http://drupal.org">drupal.org</a>

Add some text at the top of content body

This will add BEGIN: at the top of your content body.

• Pattern: /^/
• PHP Code: off
• Replacement: <strong>BEGIN:</strong><br/>

Add some text below the content body

This will add :END below your content body.

• Pattern: /$/
• PHP Code: off
• Replacement: <br/><strong>:END</strong>

Anchorize subtitles

Precedes all <h2> and <h3> tags (subtitles) with an anchor named with the sanitized title. This allows to link to a specific section of a page. An example: http://drupal.org/node/210555#anchorize-subtitles
Use your browser inspector to reveal the anchors.

• Pattern: /<h(2|3)>(.*)<\/h(2|3)>/i
• PHP Code: on
• Replacement:
  

  $name = trim(preg_replace('/[^a-z0-9]+/', '-', strtolower($matches[2])), '-');
  $result = '<p><a name="' . $name . '"></a></p>' . $matches[0];

Auto numbering mechanism

Each <an/> will be converted into sequential number 1, 2, 3, 4, ... This replacement rule is an example of numbering mechanism.

• Pattern: /<\s*an\s*\/>/i
• PHP Code: on
• Replacement:
  

  static $num;
  
  $num++;
  
  return $num;
  

Correct paths in img-tags

This will correct all absolute and relative paths in <img /> tags in your content body. It helps if you installed drupal in a sub-directory of your webroot and insert the paths as /sites/default/files.

• Pattern: /(<img[^>]+(src="([\w|\.|\/|\-|\_]+)")[^>]+\/>)/
• PHP Code: on
• Replacement: $result = str_replace($matches[3], url($matches[3]), $matches[1]);

"Intelligent" links

This will allow you to create links inside your site with automatic name. For example, you write [url==23]description for editing[/url] and you get a link like <a href="path_to_your_node">title of my node 23</a>.

• Pattern: /\[url==([\d]+)](.+?)\[\/url]/
• PHP Code: on
• Replacement:
  

  $node = node_load($matches[1]);
  if (!$node) {
      $result = '<span class="custom_filter_warning">-Node not found, check the node id you entered-</span>';
      }
  else {
      $result = l($node->title, 'node/' . $matches[1]);
      }
  return $result;

Remove inaccessible links

When an internal link would lead to access denied or not found, then the link is stripped only leaving the description text.

• Pattern: /<a\shref=\"([^\"]*)\">(.*)<\/a>/siU
• PHP Code: on
• Replacement:
  

  $link=preg_replace("/^\//","",$matches[1]);
  $result=drupal_valid_path($link)?$matches[0]:$matches[2];

Using with geshi

This is a complex example, it show how to use custom filter and the geshi library to highlight source code in pre tags.
Download the geshi library from http://qbnz.com/highlighter/ , unpack it and copy to sites/all/libraries/geshi

• Pattern: /<pre([.\s\S]*?)>([.\s\S]*?)<\/pre>/i
• PHP Code: on
• Replacement:
  

  require_once DRUPAL_ROOT . "/sites/all/libraries/geshi/geshi.php";
  
  $attr = array();
  $start = true;
  $pieces = explode("=", $matches[1]);
    
  foreach($pieces as $piece)  {
    if ($start) {
      $key = $piece;
      $start = false;
    } else {
      $p = explode('"', $piece);
        $attr[trim($key)] = $p[1];
        $key = trim($p[2]);
    }
  }
  
  
  $geshi = new GeSHi(decode_entities($matches[2]), $attr['language']);
  $geshi->set_overall_style('font-size: 1.4em;');
  $geshi->set_header_type(GESHI_HEADER_PRE_TABLE);
  
  if ($attr['lines']) {
      $geshi->enable_line_numbers(GESHI_NORMAL_LINE_NUMBERS);
      if ($attr['lines'] > 1) {
           $geshi->start_line_numbers_at($attr['lines']);
      }
  }
  $result = '<div class="geshi_code">'  . $geshi->parse_code() . '</div>';
  
  return $result;

More examples will be added soon.