PHP Regex for Developers

PHP Regex for Web Developers

Regular expressions are a very useful tool for developers. They allow to find, identify or replace a word, character or any kind of string. This tutorial will teach you how to master PHP regexp and show you extremely useful, ready-to-use PHP regular expressions that any web developer should have in his toolkit.

Getting Started With Regular Expressions

For many beginners, regular expressions seem 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 of PCRE regex patterns:

Regular Expressions Syntax

A regular expression (regex or regexp for short) is a special text string for describing a search pattern. A regex pattern matches a target string. The following table describes most common regex:

Regular ExpressionWill match…
fooThe 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 “jpg”
[a-z]+One or more lowercase letters
[0-9.-]Any 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

PHP has many useful functions to work with regular expressions. Here is a quick cheat sheet of the main PHP regex functions. Remember that all of them are case sensitive.

For more information about the native functions for PHP regular expressions, have a look at the manual.

FunctionDescription
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. Useful for search and replace.
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() Preg Split (preg_split()) operates exactly like the split() function, except that regular expressions are accepted as input parameters.
preg_grep() The preg_grep() function searches all elements of input_array, returning all elements matching the regex pattern within a string.

preg_ quote() Quote regular expression characters

 

Validate a Domain Name

Case sensitive regex to verify if a string is a valid domain name. This is very useful when validating web forms.

$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.";
}

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Enlight a Word From a Text

This very useful regular expression will find a specific word in a string and enlight it. Extremely useful for search results. Remember that it’s case sensitive.

$text = "Sample sentence... 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";
echo preg_replace("/b(regex)b/i", '<span style="background:#5fc9f6">1</span>', $text);

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Enlight Search Results in Your WordPress Blog

The previous code snippet can be very handy when it comes to displaying search results. If your website is powered by WordPress, here is a more specific snippet that will search and replace a text by the same text within an HTML tag that you can style later, using CSS.

Open your search.php file and find the the_title() function. Replace it with the following:

echo $title;

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

<?php
	$title 	= get_the_title();
	$keys= explode(" ",$s);
	$title 	= preg_replace('/('.implode('|', $keys) .')/iu',
		'<strong class="search-excerpt">\0</strong>',
		$title);
?>

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

strong.search-excerpt { background: yellow; }

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Get All Images From a HTML Document

If you ever wanted 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.

$images = array();
preg_match_all('/(img|src)=("|')[^"'>]+/i', $data, $media);
unset($data);
$data=preg_replace('/(img|src)("|'|="|=')(.*)/i',"$3",$media[0]);
foreach($data as $url)
{
	$info = pathinfo($url);
	if (isset($info['extension']))
	{
		if (($info['extension'] == 'jpg') ||
		($info['extension'] == 'jpeg') ||
		($info['extension'] == 'gif') ||
		($info['extension'] == 'png'))
		array_push($images, $url);
	}
}

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Remove Repeated Words (Case Insensitive)

Often repeating words while typing? This handy case insensitive PCRE regex will be very helpful.

$text = preg_replace("/s(w+s)1/i", "$1", $text);

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Remove Repeated Punctuation

Same php regex as above, but this one will look for repeated punctuation within a string. Goodbye multiple commas!

$text = preg_replace("/.+/i", ".", $text); 

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Match 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.

function get_tag( $tag, $xml ) {
  $tag = preg_quote($tag);
  preg_match_all('{<'.$tag.'[^>]*>(.*?)</'.$tag.'>.'}',
                   $xml,
                   $matches,
                   PREG_PATTERN_ORDER);

  return $matches[1];
}

Match an HTML/XML Tag With a Specific 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 <div id="header">.

function get_tag( $attr, $value, $xml, $tag=null ) {
  if( is_null($tag) )
    $tag = '\w+';
  else
    $tag = preg_quote($tag);

  $attr = preg_quote($attr);
  $value = preg_quote($value);

  $tag_regex = "/<(".$tag.")[^>]*$attr\s*=\s*".
                "(['\"])$value\\2[^>]*>(.*?)<\/\\1>/"

  preg_match_all($tag_regex,
                 $xml,
                 $matches,
                 PREG_PATTERN_ORDER);

  return $matches[3];
}

Match Hexadecimal Color Values

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

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

Find Page Title

This handy code snippet will find and print the text within the <title> and </title> tags of a HTML page.

$fp = fopen("https://catswhocode.com/blog","r"); 
while (!feof($fp) ){
    $page .= fgets($fp, 4096);
}

$titre = eregi("<title>(.*)</title>",$page,$regs); 
echo $regs[1];
fclose($fp);

Parse Apache Logs

Most websites are running on the Apache webserver. If your website does, you can easily use PHP and regular expressions to parse Apache logs.

//Logs: Apache web server
//Successful hits to HTML files only.  Useful for counting the number of page views.
'^((?#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)[^"]*)"$'

//Logs: Apache web server
//404 errors only
'^((?#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)[^"]*)"$'

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Replace Double Quotes by Smart Quotes

If you’re a typography lover, you’ll probably love this regex pattern which allow you to replace double quotes by smart quotes. A similar regular expression is used by WordPress to make the content more beautiful.

preg_replace('B"b([^"x84x93x94rn]+)b"B', '?1?', $text);

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Check 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 uppercase letter, one lowercase letter and one digit.

'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'

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WordPress: Using Regexp to Retrieve Images From a Post

As I know many of you are WordPress users, you’ll probably enjoy that code which allows 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.

<?php if (have_posts()) : ?>
<?php while (have_posts()) : the_post(); ?>

<?php
$szPostContent = $post->post_content;
$szSearchPattern = '~<img [^>]* />~';

// Run preg_match_all to grab all the images and save the results in $aPics
preg_match_all( $szSearchPattern, $szPostContent, $aPics );

// Check to see if we have at least 1 image
$iNumberOfPics = count($aPics[0]);

if ( $iNumberOfPics > 0 ) {
     // Now here you would do whatever you need to do with the images
     // For this example the images are just displayed
     for ( $i=0; $i < $iNumberOfPics ; $i++ ) {
          echo $aPics[0][$i];
     };
};

endwhile;
endif;
?>

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Generate Emoticons Automatically

Another function used by WordPress. This one allow you to automatically replace an emoticon symbol by an image.

$texte='A text with a smiley :-)';
echo str_replace(':-)','<img src="smileys/souriant.png">',$texte);

 

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