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PHP preg_replace() Function

❮ PHP RegExp Reference


Use a case-insensitive regular expression to replace Microsoft with W3Schools in a string:

$str = 'Visit Microsoft!';
$pattern = '/microsoft/i';
echo preg_replace($pattern, 'W3Schools', $str);
Try it Yourself »

Definition and Usage

The preg_replace() function returns a string or array of strings where all matches of a pattern or list of patterns found in the input are replaced with substrings.

There are three different ways to use this function:

1. One pattern and a replacement string. Matches of the pattern are replaced with the replacement string.

2. An array of patterns and a replacement string. Matches any of the patterns are replaced with the replacement string.

3. An array of patterns and an array of replacement strings. Matches of each pattern are replaced with the replacement string at the same position in the replacements array. If no item is found at that position the match is replaced with an empty string.

Replacement strings may contain a backreference in the form \n or $n where n is the index of a group in the pattern. In the returned string, instances of \n and $n will be replaced with the substring that was matched by the group or, if \0 or $0 are used, by the whole expression.

Note: For each input string, the function evaluates the patterns in the order that they are given. The result of evaluating the first pattern on the string is used as the input string for the second pattern and so on. This can lead to unexpected behaviour.


preg_replace(patterns, replacements, input, limit, count)

Parameter Values

Parameter Description
patterns Required. Contains a regular expression or array of regular expressions
replacements Required. A replacement string or an array of replacement strings
input Required. The string or array of strings in which replacements are being performed
limit Optional. Defaults to -1, meaning unlimited. Sets a limit to how many replacements can be done in each string
count Optional. After the function has executed, this variable will contain a number indicating how many replacements were performed

Technical Details

Return Value: Returns a string or an array of strings resulting from applying the replacements to the input string or strings
PHP Version: 4.0.5+
Changelog: PHP 5.1.0 - The count parameter was added

❮ PHP RegExp Reference