如何从不同的php文件中获取另一个变量到另一个文件？

// file1.php
$variable = "Hello, World!";

// file2.php
include 'file1.php';
echo $variable; // 输出：Hello, World!

// file1.php
session_start();
$_SESSION['variable'] = "Hello, World!";

// file2.php
session_start();
echo $_SESSION['variable']; // 输出：Hello, World!

// file1.php
$variable = "Hello, World!";
echo "<a href='file2.php?var=" . urlencode($variable) . "'>Go to file2</a>";

// file2.php
$variable = $_GET['var'];
echo $variable; // 输出：Hello, World!

// file1.php
function getVariable() {
    $variable = "Hello, World!";
    return $variable;
}

// file2.php
$variable = getVariable();
echo $variable; // 输出：Hello, World!