The logical operator xor stands for exclusive or. It takes two different boolean values or expressions as its operands and returns a single boolean value. Unlike regular or which evaluates to TRUE if either its left operand or its right operand evaluate to TRUE, xor evaluates to TRUE only if either its left operand or its right operand evaluate to TRUE, but not both.

TRUE xor TRUE;   // Evaluates to: FALSE

FALSE xor TRUE;  // Evaluates to: TRUE

TRUE xor FALSE;  // Evaluates to: TRUE

FALSE xor FALSE; // Evaluates to: FALSE

We can use xor to answer either/or questions: Did you wear either glasses or contacts today?

• If neither, the answer is “No”—I didn’t wear glasses nor did I wear contacts. My vision is impaired.
• If I wore both, the answer is “No”—I didn’t wear either glasses or contacts. My vision is impaired.
• If I wore contacts, the answer is “Yes”—I wore contacts, so my vision was corrected.
• If I wore glasses, the answer is “Yes”—I wore glasses, so my vision was corrected. .

Let’s code up this example:

$is_wearing_glasses = TRUE;
$is_wearing_contacts = TRUE;

if ($is_wearing_glasses xor $is_wearing_contacts){
    echo "Your vision is corrected!";
} else {
    echo "Your vision is impaired.";
}

Let’s practice!