check session availability in PHP

session.php

<?php

session_start();

$sessPath   = ini_get('session.save_path');
$sessCookie = ini_get('session.cookie_path');
$sessName   = ini_get('session.name');
$sessVar    = 'foo';
$essValue   = 'hello world';

echo '<br>sessPath: ' . $sessPath;
echo '<br>sessCookie: ' . $sessCookie;
echo '<hr>';

$action = isset($_GET['action']) ? $_GET['action'] : 0;
if( $action == 1 ){
    $_SESSION[$sessVar] = $essValue;
    echo 'Session key ' . $sessVar . ' was set';
    echo '<br>'.$sessVar . ': ' . $essValue;

}elseif( $action == 2 ){
    // printing session value and global cookie PHPSESSID
    echo $sessVar . ': ';
    if( isset( $_SESSION[$sessVar] ) ){
        echo $_SESSION[$sessVar];
    }else{
        echo '[not exists]';
    }

    echo '<br>' . $sessName . ': ';

    if( isset( $_COOKIE[$sessName] ) ){
        echo $_COOKIE[$sessName];
    }else{
        if( isset( $_REQUEST[$sessName] ) ){
            echo $_REQUEST[$sessName];
        }else{
            if( isset( $_SERVER['HTTP_COOKIE'] ) ){
                echo $_SERVER['HTTP_COOKIE'];
            }else{
                echo 'problem, check your PHP settings';
            }
        }
    }

} elseif( $action == 3 ){
    // destroy session by unset() function
    echo 'Try to unset session key «'.$sessVar.'»';
    unset( $_SESSION[$sessVar] );
    // check if was destroyed
    if( !isset( $_SESSION[$sessVar] ) ){
        echo '<br>'.$sessName . ' was "unseted"';
    }else{
        echo '<br>'.$sessName . ' was not "unseted"';
    }
}

?>
<hr>
<a href=<?php echo basename(__FILE__) ?>?action=1>Define value in session</a><br />
<a href=<?php echo basename(__FILE__) ?>?action=2>Printing value from session</a><br />
<a href=<?php echo basename(__FILE__) ?>?action=3>Remove value in session</a><br />