Redirect user if not logged in.

wp.snippet

/**
* Snippet Action: Redirect user if not logged in. 
* Snippet Author: Keith Crain ( MainWP.com )
*/

function custom_template_redirect_fn()
{
    if( ! is_user_logged_in ) {
    {
        $loginUrl = wp_login_url();
        wp_redirect( $loginUrl );
        exit(); 
    }

}
add_action( 'template_redirect', 'custom_template_redirect_fn' );