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# preg_replace

preg_replace -- Perform a regular expression search and replace

## Description

`mixed preg_replace`(mixed pattern, mixed replacement, mixed subject);

Searches `subject` for matches to `pattern` and replaces them with `replacement` .

`replacement` may contain references of the form `\\`n``. 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` 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.

If no matches are found in `subject`, then it will be returned unchanged.

Every parameter to preg_replace() can be an array.

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().

> Note: This modifier was added in PHP 4.0.

Example 1. Replacing several values
    $patterns = array("/(19|20\d{2})-(\d{1,2})-(\d{1,2})/", "/^\s*{(\w+)}\s*=/");
    $replace = array("\\3/\\4/\\1", "$\\1 =");
    print preg_replace($patterns, $replace, "{startDate} = 1999-5-27");

This example will produce:

          $startDate = 5/27/1999

Example 2. Using /e modifier
    preg_replace("/(<\/?)(\w+)([^>]*>)/e", "'\\1'.strtoupper('\\2').'\\3'", $html_body);
This would capitalize all HTML tags in the input text.

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

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