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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.

Exemplo 1. Using backreferences followed by numeric literals

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

This example will 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 unidimensional 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().

Exemplo 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"; $replacements[0] = "slow"; echo preg_replace($patterns, $replacements, $string); ?>`

Output:

    The bear black slow jumped over the lazy dog.

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

`<?php ksort($patterns); ksort($replacements); echo 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().

Exemplo 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 ="); echo preg_replace($patterns, $replace, "{startDate} = 1999-5-27"); ?>`

This example will produce:

    $startDate = 5/27/1999

Exemplo 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.

Exemplo 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);
?>`

> Nota: Parameter `limit` was added after PHP 4.0.1pl2.

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

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