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preg_replace

(PHP 3>= 3.0.9, PHP 4 )

preg_replace -- Perform a regular expression search and replace

Description

mixed preg_replace ( mixed pattern, mixed replacement, mixed subject [, int limit])

Searches subject for matches to pattern and replaces them with replacement. If limit is specified, then only limit matches will be replaced; if limit is omitted or is -1, then all matches are replaced.

Replacement may contain references of the form \\n or (since PHP 4.0.4) $n, with the latter form being the preferred one. Every such reference will be replaced by the text captured by the n'th parenthesized pattern. n can be from 0 to 99, and \\0 or $0 refers to the text matched by the whole pattern. Opening parentheses are counted from left to right (starting from 1) to obtain the number of the capturing subpattern.

When working with a replacement pattern where a backreference is immediately followed by another number (i.e.: placing a literal number immediately after a matched pattern), you cannot use the familiar \\1 notation for your backreference. \\11, for example, would confuse preg_replace() since it does not know whether you want the \\1 backreference followed by a literal 1, or the \\11 backreference followed by nothing. In this case the solution is to use \${1}1. This creates an isolated $1 backreference, leaving the 1 as a literal.

Example 1. Using backreferences followed by numeric literals

<?php
$string = "April 15, 2003";
$pattern = "/(\w+) (\d+), (\d+)/i";
$replacement = "\${1}1,\$3";
print preg_replace($pattern, $replacement, $string);

/* Output
   ======

April1,2003

 */
 ?>

If matches are found, the new subject will be returned, otherwise subject will be returned unchanged.

Every parameter to preg_replace() (except limit) can be an array. When using arrays with pattern and replacement, the keys are processed in the order they appear in the array. This is not necessarily the same as the numerical index order. If you use indexes to identify which pattern should be replaced by which replacement, you should perform a ksort() on each array prior to calling preg_replace().

Example 2. Using indexed arrays with preg_replace()

<?php
$string = "The quick brown fox jumped over the lazy dog.";

$patterns[0] = "/quick/";
$patterns[1] = "/brown/";
$patterns[2] = "/fox/";

$replacements[2] = "bear";
$replacements[1] = "black";
$replacements[0] = "slow";

print preg_replace($patterns, $replacements, $string);

/* Output
   ======

The bear black slow jumped over the lazy dog.

*/

/* By ksorting patterns and replacements,
   we should get what we wanted. */

ksort($patterns);
ksort($replacements);

print preg_replace($patterns, $replacements, $string);

/* Output
   ======

The slow black bear jumped over the lazy dog.

*/

 ?>

If subject is an array, then the search and replace is performed on every entry of subject, and the return value is an array as well.

If pattern and replacement are arrays, then preg_replace() takes a value from each array and uses them to do search and replace on subject. If replacement has fewer values than pattern, then empty string is used for the rest of replacement values. If pattern is an array and replacement is a string, then this replacement string is used for every value of pattern. The converse would not make sense, though.

/e modifier makes preg_replace() treat the replacement parameter as PHP code after the appropriate references substitution is done. Tip: make sure that replacement constitutes a valid PHP code string, otherwise PHP will complain about a parse error at the line containing preg_replace().

Example 3. Replacing several values

<?php
$patterns = array ("/(19|20)(\d{2})-(\d{1,2})-(\d{1,2})/",
                   "/^\s*{(\w+)}\s*=/");
$replace = array ("\\3/\\4/\\1\\2", "$\\1 =");
print preg_replace ($patterns, $replace, "{startDate} = 1999-5-27");
 ?>

This example will produce:

$startDate = 5/27/1999

Example 4. Using /e modifier

<?php
preg_replace ("/(<\/?)(\w+)([^>]*>)/e", 
              "'\\1'.strtoupper('\\2').'\\3'", 
              $html_body);
 ?>

This would capitalize all HTML tags in the input text.

Example 5. Convert HTML to text

<?php
// $document should contain an HTML document.
// This will remove HTML tags, javascript sections
// and white space. It will also convert some
// common HTML entities to their text equivalent.

$search = array ("'<script[^>]*?>.*?</script>'si",  // Strip out javascript
                 "'<[\/\!]*?[^<>]*?>'si",           // Strip out html tags
                 "'([\r\n])[\s]+'",                 // Strip out white space
                 "'&(quot|#34);'i",                 // Replace html entities
                 "'&(amp|#38);'i",
                 "'&(lt|#60);'i",
                 "'&(gt|#62);'i",
                 "'&(nbsp|#160);'i",
                 "'&(iexcl|#161);'i",
                 "'&(cent|#162);'i",
                 "'&(pound|#163);'i",
                 "'&(copy|#169);'i",
                 "'&#(\d+);'e");                    // evaluate as php

$replace = array ("",
                  "",
                  "\\1",
                  "\"",
                  "&",
                  "<",
                  ">",
                  " ",
                  chr(161),
                  chr(162),
                  chr(163),
                  chr(169),
                  "chr(\\1)");

$text = preg_replace ($search, $replace, $document);
 ?>

Note: Parameter limit was added after PHP 4.0.1pl2.

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

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