PHP Guru: 15 PHP regular expressions for web developers (Regex)

Getting started with regular expressions

For many beginners, regular expressions seems to be hard to learn and use. In fact, they’re far less hard than you may think. Before we dive deep inside regexp with useful and reusable codes, let’s quickly see the basics:

Regular expressions syntax

Regular Expression	Will match…
foo	The string “foo”
^foo	“foo” at the start of a string
foo$	“foo” at the end of a string
^foo$	“foo” when it is alone on a string
[abc]	a, b, or c
[a-z]	Any lowercase letter
[^A-Z]	Any character that is not a uppercase letter
(gif\|jpg)	Matches either “gif” or “jpeg”
[a-z]+	One or more lowercase letters
[0-9.-]	Ðny number, dot, or minus sign
^[a-zA-Z0-9_]{1,}$	Any word of at least one letter, number or _
([wx])([yz])	wy, wz, xy, or xz
[^A-Za-z0-9]	Any symbol (not a number or a letter)
([A-Z]{3}\|[0-9]{4})	Matches three letters or four numbers

PHP regular expression functions

Function	Description
preg_match()	The preg_match() function searches string for pattern, returning true if pattern exists, and false otherwise.
preg_match_all()	The preg_match_all() function matches all occurrences of pattern in string.
preg_replace()	The preg_replace() function operates just like ereg_replace(), except that regular expressions can be used in the pattern and replacement input parameters.
preg_split()	The preg_split() function operates exactly like split(), except that regular expressions are accepted as input parameters for pattern.
preg_grep()	The preg_grep() function searches all elements of input_array, returning all elements matching the regexp pattern.
preg_ quote()	Quote regular expression characters

Validate domain name

Verify if a string is a valid domain name.

$url = "http://komunitasweb.com/";
if (preg_match('/^(http|https|ftp)://([A-Z0-9][A-Z0-9_-]*(?:.[A-Z0-9][A-Z0-9_-]*)+):?(d+)?/?/i', $url)) {
    echo "Your url is ok.";
} else {
    echo "Wrong  url.";
}

» Source

Enlight a word from a text

This very useful regular expression find a specific word in a text, and enlight it. Extremely useful for search results.

$text = "Sample sentence from KomunitasWeb, regex has become  popular in web programming. Now we learn regex. According to wikipedia,  Regular expressions (abbreviated as regex or regexp, with plural forms  regexes, regexps, or regexen) are written in a formal language that can  be interpreted by a regular expression processor";
$text  = preg_replace("/b(regex)b/i", '1',  $text);
echo $text;

» Source

Enlight search results in your WordPress blog

As I just said that the previous code snippet could be very handy on search results, here is a great way to implement it on a WordPress blog.
Open your search.php file and find the the_title() function. Replace it with the following:

1.echo $title;

Now, just before the modified line, add this code:

1.

2.    $title  =  get_the_title();
3.    $keys= explode(" ",$s);
4.    $title  =  preg_replace('/('.implode('|', $keys) .')/iu',
5.        '\0',
6.        $title);
7.?>

Save  the search.php file and open style.css. Append the  following line to it:

strong.search-excerpt { background: yellow; }
»  Source

Get  all images from a HTML document
If you ever widhed to be able to  get all images form a webpage, this code is a must have for you. You  should easily create an image downloader using the power of cURL.

view  source
print?
01.$images = array();
02.preg_match_all('/(img|src)=("|')[^"'>]+/i', $data, $media);
03.unset($data);
04.$data=preg_replace('/(img|src)("|'|="|=')(.*)/i',"$3",$media[0]);
05.foreach($data as $url)
06.{
07.    $info = pathinfo($url);
08.    if (isset($info['extension']))
09.    {
10.        if (($info['extension'] == 'jpg') ||
11.        ($info['extension'] == 'jpeg') ||
12.        ($info['extension'] == 'gif') ||
13.        ($info['extension'] == 'png'))
14.        array_push($images, $url);
15.    }
16.}
»  Source

Remove repeated words (case  insensitive)
Often repeating words while typing? This handy  regexp will be very helpful.

view  source
print?
1.$text =  preg_replace("/s(w+s)1/i", "$1", $text);
» Source

Remove repeated punctuation
Same  as above, but with punctuation. Goodbye repeated commas!

view  source
print?
1.$text =  preg_replace("/.+/i", ".", $text);
» Source

Matching a XML/HTML tag
This  simple function takes two arguments: The first is the tag you’d like to  match, and the second is the variable containing the XML or HTML. Once  again, this can be very powerful used along with cURL.

view  source
print?
01.function get_tag(  $tag, $xml ) {
02.  $tag =  preg_quote($tag);
03.  preg_match_all('{<'.$tag.'[^>]*>(.*?).$tag.'>.'}',
04.                   $xml,
05.                   $matches,
06.                   PREG_PATTERN_ORDER);
07. 
08.  return $matches[1];
09.}
»  Source

Matching an XHTML/XML tag  with a certain attribute value
This function is very similar to  the previous one, but it allow you to match a tag having a specific  attribute. For example, you could easily match 

.

view  source
print?
01.function get_tag(  $attr, $value, $xml, $tag=null ) {
02.  if( is_null($tag) )
03.    $tag = '\w+';
04.  else
05.    $tag =  preg_quote($tag);
06. 
07.  $attr =  preg_quote($attr);
08.  $value =  preg_quote($value);
09. 
10.  $tag_regex =  "/<(".$tag.")[^>]*$attr\s*=\s*".
11.                "(['\"])$value\\2[^>]*>(.*?)<\/\\1>/"
12. 
13.  preg_match_all($tag_regex,
14.                 $xml,
15.                 $matches,
16.                 PREG_PATTERN_ORDER);
17. 
18.  return $matches[3];
19.}
»  Source

Matching hexadecimal color  values
Another interesting tool for web developers! It allows you  to match/validate a hexadecimal color value.

view  source
print?
1.$string = "#555555";
2.if (preg_match('/^#(?:(?:[a-fd]{3}){1,2})$/i',  $string)) {
3.echo "example 6  successful.";
4.}
»  Source

Find page title
This  handy code snippet will find and print the text within the  tags of a html page.

view  source
print?
1.$fp = fopen("http://www.catswhocode.com/blog","r");
2.while  (!feof($fp) ){
3.    $page .= fgets($fp, 4096);
4.}
5. 
6.$titre = eregi("",$page,$regs);
7.echo  $regs[1];
8.fclose($fp);


Parsing  Apache logs
Most websites are running on the well-known Apache  webserver. If your website does, what about using PHP and some regular  expressions to parse Apache logs?

view  source
print?
1.//Logs: Apache web server
2.//Successful hits to HTML files only.  Useful for  counting the number of page views.
3.'^((?#client IP or domain name)S+)s+((?#basic  authentication)S+s+S+)s+[((?#date and time)[^]]+)]s+"(?:GET|POST|HEAD)  ((?#file)/[^ ?"]+?.html?)??((?#parameters)[^ ?"]+)?  HTTP/[0-9.]+"s+(?#status code)200s+((?#bytes  transferred)[-0-9]+)s+"((?#referrer)[^"]*)"s+"((?#user agent)[^"]*)"$'
4. 
5.//Logs: Apache web server
6.//404 errors only
7.'^((?#client IP or domain name)S+)s+((?#basic  authentication)S+s+S+)s+[((?#date and time)[^]]+)]s+"(?:GET|POST|HEAD)  ((?#file)[^ ?"]+)??((?#parameters)[^ ?"]+)? HTTP/[0-9.]+"s+(?#status  code)404s+((?#bytes  transferred)[-0-9]+)s+"((?#referrer)[^"]*)"s+"((?#user agent)[^"]*)"$'
»  Source

Replacing double quotes by  smart qutotes
If you’re a typographer lover, you’ll probably love  this regexp, which allow you to replace normal double quotes by smart  quotes. A regular expression of that kind is used by WordPress on  contents.

view  source
print?
1.preg_replace('B"b([^"x84x93x94rn]+)b"B', '?1?', $text);
» Source

Checking password complexity
This  regular expression will tests if the input consists of 6 or more  letters, digits, underscores and hyphens.

The input must contain at  least one upper case letter, one lower case letter and one digit.

view  source
print?
1.'A(?=[-_a-zA-Z0-9]*?[A-Z])(?=[-_a-zA-Z0-9]*?[a-z])(?=[-_a-zA-Z0-9]*?[0-9])[-_a-zA-Z0-9]{6,}z'
»  Source

WordPress: Using regexp to  retrieve images from post
As I know many of you are WordPress  users, you’ll probably enjoy that code which allow you to retrieve all  images from post content and display it.

To use this code on your  blog, simply paste the following code on one of your theme files.

view  source
print?
01.if  (have_posts()) : ?>
02.while (have_posts())  : the_post(); ?>
03. 
04.
05.$szPostContent = $post->post_content;
06.$szSearchPattern = '~]* />~';
07. 
08.// Run preg_match_all to grab all the images and save  the results in $aPics
09.preg_match_all(  $szSearchPattern, $szPostContent, $aPics );
10. 
11.// Check to see if we have at least 1 image
12.$iNumberOfPics = count($aPics[0]);
13. 
14.if ( $iNumberOfPics > 0 ) {
15.     // Now here you would do whatever  you need to do with the images
16.     // For this example the images are  just displayed
17.     for ( $i=0; $i < $iNumberOfPics ; $i++ ) {
18.          echo $aPics[0][$i];
19.     };
20.};
21. 
22.endwhile;
23.endif;
24.?>
»  Source

Generating automatic smileys
Another  function used by WordPress, this one allow you to automatically replace  a smiley symbol by an image.

view  source
print?
1.$texte='A text with a smiley :-)';
2.echo str_replace(':-)','',$texte);

PHP Guru

Wednesday, March 3, 2010

15 PHP regular expressions for web developers (Regex)

Getting started with regular expressions

Regular expressions syntax

PHP regular expression functions

Validate domain name

Enlight a word from a text

Enlight search results in your WordPress blog

Get all images from a HTML document

Remove repeated words (case insensitive)

Remove repeated punctuation

Matching a XML/HTML tag

Matching an XHTML/XML tag with a certain attribute value

Matching hexadecimal color values

Find page title

Parsing Apache logs

Replacing double quotes by smart qutotes

Checking password complexity

WordPress: Using regexp to retrieve images from post

Generating automatic smileys

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