What is the difference between using single quotes ('') and double quotes ("") in PHP?

In PHP, single quotes ('') and double quotes ("") are used to define strings. The main difference between the two is that double quotes allow for the interpretation of variables and special characters within the string, while single quotes do not. When using double quotes, PHP will parse the string and replace variables with their values, whereas single quotes will treat everything literally. To fix this issue, you can use double quotes when you want PHP to interpret variables within the string. If you want to use single quotes but still include variables, you can concatenate the variables outside the quotes using the dot (.) operator.

// Using double quotes to interpret variables within the string
$name = "John";
echo "Hello, $name!";

// Using single quotes and concatenation for variables
$name = "John";
echo 'Hello, ' . $name . '!';