The preg_replace() function is an inbuilt function in PHP that is used to perform a regular expression for search and replace the content.

 Syntax:

preg_replace( $pattern, $replacement, $subject, $limit, $count )

Parameters: This function accepts five parameters as mentioned above and described below.

• $pattern: This parameter contains the string element which is used to search the content and it can be a string or array of strings.
• $replacement: It is a mandatory parameter that specifies the string or an array with strings to replace.
• $subject: The string or an array with strings to search and replace.
• $limit: This parameter specifies the maximum possible replacements for each pattern.
• $count: It is an optional parameter. This variable will be filled with the number of replacements done.

Return Value: This function returns an array if the subject parameter is an array, or a string otherwise. The below programs illustrate the preg_replace() function in PHP.

Program 1: The following program replaces string by using the regular expression parameter.

<?php

// PHP program to illustrate 
// preg_replace function

$string = 'November 01, 2018';
$pattern = '/(\w+) (\d+), (\d+)/i';
$replacement = '${1} 02, $3';

// print output of function
echo preg_replace($pattern, $replacement, $string);
?>

November 02, 2018

Program 2 : 

<?php

// PHP program to illustrate 
// preg_replace function
$subject = array('1', 'GFG', '2',
'Geeks', '3', 'GCET', 'Contribute', '4'); 
$pattern = array('/\d/', '/[a-z]/', '/[1a]/'); 
$replace = array('X:$0', 'Y:$0', 'Z:$0'); 

// Print Result return by function
echo "preg_replace returns\n";
print_r(preg_replace($pattern, $replace, $subject)); 
?>

preg_replace returns
Array
(
    [0] => X:Z:1
    [1] => GFG
    [2] => X:2
    [3] => GY:eY:eY:kY:s
    [4] => X:3
    [5] => GCET
    [6] => CY:oY:nY:tY:rY:iY:bY:uY:tY:e
    [7] => X:4
)

Program 3: 

<?php

// PHP program to illustrate 
// preg_replace function
$count = 0;

// Display result after replace and count 
echo preg_replace(array('/\d/', '/\s/'),
        '*', 'Geeks 4 Geeks', -1, $count);
echo "\n" . $count;
?>

Geeks***Geeks
3

Reference: http://php.net/manual/en/function.preg-replace.php