Fetch btc exchange rate

bc_exchange.php

<?php
/**
 * @package bc_exchange
 * @version 1.2
 */
/*
Plugin Name: BC Exchange
Plugin URI: https://github.com/devpilot/
Description: Get BTC Exchange rate from <a href="https://blockchain.info/">Blockchain</a>
Author: DevPilot
Version: 1.2
Author URI: https://github.com/devpilot/
*/

/* Usage: [bcex currency=USD] */

/**
 * Fetch exchange rate
 *
 * @author 	DevPilot
 */
class Ex_Rate {
	/**
     * Exchange data.
     *
     * @since    1.0.0
     * @access   private
     * @var      string    $exData    exchange data in json.
     */
	private $exData;

	public function __construct() {
		$this->exData = file_get_contents('https://blockchain.info/ticker');
	}
	// Add Shortcode
	public function bcex_shortcode( $atts ) {
		// Attributes
		$atts = shortcode_atts(
			array(
				'currency' => 'USD',
			),
			$atts
		);
		if ($this->exData) {
			$values = json_decode($this->exData);
			$symb = $atts['currency'];
			return $values->$symb->last;
		}
	}
}

$ex = new Ex_Rate;
add_shortcode( 'bcex', array( $ex, 'bcex_shortcode' ) );

?>