strstr() and stristr both are used to find the first occurence of the string but stristr( ) is case insensitive.

strstr() – Find first occurrence of a string
Syntax:
strstr ($string, string)

Example:

<?php
$email = ‘rajesh@tEst.com’;
$domain_name = strstr($email, ‘E’);
echo $domain_name;

?>

Output:Est.com

stristr() – Find first occurrence of a string (Case-insensitive)
Syntax:
stristr ($string, string)

Example:
<?php
$email = ‘rajesh@tEst.com’;
$domain_name = stristr($email, ‘E’);
echo $domain_name;

?>
Output: esh@tEst.com