What is the difference between the | and || or operators?

In PHP, the "|" and "||" operators are both bitwise and logical operators. The "|" operator is a bitwise OR operator, and the "||" operator is a logical OR operator.

The difference between these two operators is in the way they evaluate the expressions on either side of them. The bitwise OR operator "|" compares each bit of the first expression to the corresponding bit of the second expression and returns a result in which each bit is set to 1 if either of the corresponding bits is set to 1.

The logical OR operator "||" evaluates the expressions on either side of it and returns a boolean value of true if either of the expressions is true, and false if both expressions are false.

Here is an example to illustrate the difference between these two operators:

<?php

$a = 4; // binary equivalent is 100
$b = 5; // binary equivalent is 101

$c = $a | $b; // performs a bitwise OR operation, resulting in 101 (decimal 5)
$d = $a || $b; // performs a logical OR operation, resulting in true

echo "a = $a (binary " . decbin($a) . ")\n";
echo "b = $b (binary " . decbin($b) . ")\n";
echo "a | b = $c (binary " . decbin($c) . ")\n";
echo "a || b = " . ($d ? 'true' : 'false') . "\n";

In this example, the variable $a is assigned the decimal value 4, which has a binary equivalent of 100. The variable $b is assigned the decimal value 5, which has a binary equivalent of 101.

The variable $c is then assigned the result of performing a bitwise OR operation on $a and $b, which results in the binary value 101 (decimal 5). The binary representation of $c is also shown using the decbin() function.

The variable $d is then assigned the result of performing a logical OR operation on $a and $b, which results in the boolean value true. The boolean value of $d is output using a ternary operator to display either "true" or "false".

When this code is run, the output will be:

a = 4 (binary 100)
b = 5 (binary 101)
a | b = 5 (binary 101)
a || b = true

This output shows the original values of $a and $b in both decimal and binary format, the result of the bitwise OR operation on $a and $b (also in both decimal and binary format), and the result of the logical OR operation on $a and $b.