The str_replace() is the built-in function in PHP and is used to replace all the characters in a string. This function is case-sensitive, if need to perform case-insensitive match and replace we can use str_ireplace() function.

The str_replace() function works by the following rules :

• If a string to be searched is that the array, it returns an array.
• If a string to be searched is that the array, find and replace is performed with an each array element.
• If both find and replace are arrays, and replace has fewer elements than find, the empty string are used as a replacement.
• If the finding value is an array, and replacement is that the string, the replacement string are used for each find value.

Syntax:

str_replace(find, replace, string, count)

find – The find parameter is required, and it specifies the value to find.

replace – The replace parameter is required, and it specifies the value to replace the value in find.

string – The string parameter is required, and it specifies the string to be searched.

Count – The count parameter is optional, and it is the variable that counts the number of replacements.

Example:

<?php
$str = 'Welcome to HTML Tutorials';
 
// Display replaced string
echo str_replace("HTML", "PHP", $str);
echo '<br>';
echo str_ireplace("html", "PHP", $str);
?>