Returns all of haystack starting from and including the first
   occurrence of needle to the end.
  
haystackThe string to search in
needle
  If needle is not a string, it is converted
  to an integer and applied as the ordinal value of a character.
  This behavior is deprecated as of PHP 7.3.0, and relying on it is highly
  discouraged. Depending on the intended behavior, the
  needle should either be explicitly cast to string,
  or an explicit call to chr() should be performed.
 
before_needle
       If TRUE, stristr()
       returns the part of the haystack before the
       first occurrence of the needle (excluding needle).
      
   needle and haystack
   are examined in a case-insensitive manner.
  
   Returns the matched substring. If needle is not
   found, returns FALSE.
  
| Version | Description | 
|---|---|
| 5.3.0 | Added the optional parameter before_needle. | 
Example #1 stristr() example
<?php
  $email = 'USER@EXAMPLE.com';
  echo stristr($email, 'e'); // outputs ER@EXAMPLE.com
  echo stristr($email, 'e', true); // As of PHP 5.3.0, outputs US
?>
Example #2 Testing if a string is found or not
<?php
  $string = 'Hello World!';
  if(stristr($string, 'earth') === FALSE) {
    echo '"earth" not found in string';
  }
// outputs: "earth" not found in string
?>
Example #3 Using a non "string" needle
<?php
  $string = 'APPLE';
  echo stristr($string, 97); // 97 = lowercase a
// outputs: APPLE
?>
Note: This function is binary-safe.