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Php preg match () function

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    (PHP 3>= 3.0.9, PHP 4 , PHP 5)
preg_match -- Perform a regular expression match
Syntax
mixed preg_match ( string pattern, string subject [, array &matches [, int flags [, int offset]]] )


     Searches subject for a match to the regular
     expression given in pattern.
    

     If matches is provided, then it is filled with the
     results of search. $matches[0] will contain the text
     that matched the full pattern, $matches[1] will have
     the text that matched the first captured parenthesized subpattern, and so
     on.
    

     flags can be the following flag:
     
PREG_OFFSET_CAPTURE

         If this flag is passed, for every occurring match the appendant string
         offset will also be returned. Note that this changes the return value
         in an array where every element is an array consisting of the matched
         string at offset 0 and its string offset into
         subject at offset 1. This
         flag is available since PHP 4.3.0 .
        

     The flags parameter is available since
     PHP 4.3.0.
    

     Normally, the search starts from the beginning of the subject string. The
     optional parameter offset can be used to specify
     the alternate place from which to start the search.
     The offset parameter is available since
     PHP 4.3.3.
    
Note: 
      Using offset is not equivalent to
      passing substr($subject, $offset) to
      preg_match() in place of the subject string, because
      pattern can contain assertions such as
      ^, $ or
      (?<=x). Compare:
     

<?php
$subject = "abcdef";
$pattern = '/^def/';
preg_match($pattern, $subject, $matches, PREG_OFFSET_CAPTURE, 3);
print_r($matches);
?>


The above example will output:
Array
(
)

       while this example
      

<?php
$subject = "abcdef";
$pattern = '/^def/';
preg_match($pattern, substr($subject,3), $matches, PREG_OFFSET_CAPTURE);
print_r($matches);
?>



       will produce
      
Array
(
    [0] => Array
        (
            [0] => def
            [1] => 0
        )

)

     preg_match() returns the number of times 
     pattern matches. That will be either 0 times
     (no match) or 1 time because preg_match() will stop
     searching after the first match. preg_match_all()
     on the contrary will continue until it reaches the end of 
     subject.
     preg_match() returns FALSE if an error occurred.
    
Tip: 
      Do not use preg_match() if you only want to check if
      one string is contained in another string. Use
      strpos() or strstr() instead as
      they will be faster.
     

     
Example 1. Find the string of text "php"

<?php
// The "i" after the pattern delimiter indicates a case-insensitive search
if (preg_match("/php/i", "PHP is the web scripting language of choice.")) {
    echo "A match was found.";
} else {
    echo "A match was not found.";
}
?>



    

     
Example 2. Find the word "web"

<?php
/* The \b in the pattern indicates a word boundary, so only the distinct
 * word "web" is matched, and not a word partial like "webbing" or "cobweb" */
if (preg_match("/\bweb\b/i", "PHP is the web scripting language of choice.")) {
    echo "A match was found.";
} else {
    echo "A match was not found.";
}

if (preg_match("/\bweb\b/i", "PHP is the website scripting language of choice.")) {
    echo "A match was found.";
} else {
    echo "A match was not found.";
}
?>



    

     
Example 3. Getting the domain name out of a URL

<?php
// get host name from URL
preg_match("/^(http:\/\/)?([^\/]+)/i",
    "http://www.php.net/index.html", $matches);
$host = $matches[2];

// get last two segments of host name
preg_match("/[^\.\/]+\.[^\.\/]+$/", $host, $matches);
echo "domain name is: {$matches[0]}\n";
?>



       This example will produce:
      
domain name is: php.net

    

     See also preg_match_all(), 
     preg_replace(), and
     preg_split().
    



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Php preg match  syntax tutorial



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