What is the scope of variables in PHP scripts and how does it affect their availability within the script?

In PHP, variables have different scopes depending on where they are declared within a script. The scope of a variable determines where it can be accessed and modified within the script. Variables declared outside of any function or class have a global scope and can be accessed anywhere in the script. Variables declared within a function have a local scope and can only be accessed within that function unless explicitly declared as global.

// Global variable
$globalVar = "I am a global variable";

function testFunction() {
    // Local variable
    $localVar = "I am a local variable";

    echo $localVar; // This will output "I am a local variable"
    echo $globalVar; // This will cause an error as $globalVar is not in the local scope
}

testFunction();
echo $globalVar; // This will output "I am a global variable"