Do a case-insensitive search for "w3schools" in a string

                
                    <?php
                    $str = "Visit W3Schools";
                    $pattern = "/w3schools/i";
                    echo preg_match($pattern, $str); 
                    ?>
                
                

Do a case-insensitive count of the number of occurrences of "ain" in a string

                
                    <?php
                    $str = "The rain in SPAIN falls mainly on the plains.";
                    $pattern = "/ain/i";
                    echo preg_match_all($pattern, $str);
                    ?>
                
                

Replace "Microsoft" with "W3Schools" in a string

                
                    <?php
                    $str = "Visit Microsoft!";
                    $pattern = "/microsoft/i";
                    echo preg_replace($pattern, "W3Schools", $str);
                    ?>