Product Attribute – How to Update from Magento 2 Root Folder

Credit to @VishwasBhatnagar for the code - I'm just clarifying what I believe the finished code should be, to do all products (the to-and-fro in the comments was getting a bit confusing I think).

<?php

ini_set('display_errors', 'On');
error_reporting(E_ALL);

require('app/Mage.php'); // this is assuming your script is located in the Magento root dir
Mage::app(); // initiate the Magento engine

$products = Mage::getModel('catalog/product')->getCollection();

foreach($products as $product)
{
    $product->setNewStock('2000-01-01');
    // this line might not be required - compare results with & without it 
    $product->setNewStockIsFormated(true);
    $product->getResource()->saveAttribute($product, 'new_stock');
}
?>

Developed a module for email setup by referring the blog for the requirement: https://webkul.com/blog/magento-2-send-transactional-email-programmatically-in-your-custom-module/

Here I have modified the helper class according the usage as follows:

<?php
namespace VendorName\CustomModule\Helper;

use Magento\Framework\App\Area;

class Emailreport extends \Magento\Framework\App\Helper\AbstractHelper
{
    /**
    * @var \Magento\Framework\App\Config\ScopeConfigInterface
    */
    protected $_scopeConfig;
    /**
    * Store manager
    *
    * @var \Magento\Store\Model\StoreManagerInterface
    */
    protected $_storeManager;
    /**
    * @var \Magento\Framework\Translate\Inline\StateInterface
    */
    protected $inlineTranslation;
    /**
    * @var \Magento\Framework\Mail\Template\TransportBuilder
    */
    protected $_transportBuilder;

    /**
    * @param Magento\Framework\App\Helper\Context $context
    * @param Magento\Framework\App\Config\ScopeConfigInterface $scopeConfig
    * @param Magento\Store\Model\StoreManagerInterface $storeManager
    * @param Magento\Framework\Translate\Inline\StateInterface $inlineTranslation
    * @param Magento\Framework\Mail\Template\TransportBuilder $transportBuilder
    */
    public function __construct(
        \Magento\Framework\App\Helper\Context $context,
        \Magento\Store\Model\StoreManagerInterface $storeManager,
        \Magento\Framework\Translate\Inline\StateInterface $inlineTranslation,
        \Magento\Framework\Mail\Template\TransportBuilder $transportBuilder,
        \Magento\Framework\App\State $state
        ) {
        $this->_scopeConfig = $context;
        parent::__construct($context);
        $this->_storeManager = $storeManager;
        $this->inlineTranslation = $inlineTranslation;
        $this->_transportBuilder = $transportBuilder;
        $state->setAreaCode('frontend');
    }
    /**
    * @param string $path
    * @param int $storeId
    * @return mixed
    */
    protected function getConfigValue($path, $storeId)
    {
        return $this->scopeConfig->getValue(
            $path,
            \Magento\Store\Model\ScopeInterface::SCOPE_STORE,
            $storeId
            );
    }
    /**
    * Return store
    *
    * @return Store
    */
    public function getStore()
    {
        return $this->_storeManager->getStore();
    }

    public function sendEmailReport(
        $template,
        $senderInfo,
        $receiverInfo,
        $templateParams = []
        ) {
        $this->inlineTranslation->suspend();
        $templateId = $this->getConfigValue($template, $this->getStore()->getStoreId());

        $transport = $this->_transportBuilder->setTemplateIdentifier($templateId)
        ->setTemplateOptions(
            [
            'area' => Area::AREA_FRONTEND,
            'store' => $this->getStore()->getId(),
            ]
            )
        ->setTemplateVars($templateParams)
        ->setFrom($senderInfo)
        ->addTo($receiverInfo['email'],$receiverInfo['name'])
        ->getTransport();

        $transport->sendMessage();
        $this->inlineTranslation->resume();

        return $this;
    }
}

Now using the following code we can able to trigger the email from root folder:

<?php 
use \Magento\Framework\App\Bootstrap;
require __DIR__ . '/app/bootstrap.php';
$bootstrap = Bootstrap::create(BP, $_SERVER);
$objectManager = $bootstrap->getObjectManager();

$customEmailPath = 'contact/email/email_template'; // section_id/group_id/field_id

/* Sender Detail */
$senderInfo = [
'name' => 'sender',
'email' => 'sender@domain.com'
];

/* Receiver Detail */
$receiverInfo = [
'name' => 'receiver',
'email' => 'receiver@domain.com'
];

/* To assign the values to template variables */

$customerDetails = array();
$customerDetails['name'] = 'John Doe';
$customerDetails['email'] = 'test@example.com';



$objectManager->get('VendorName\CustomModule\Helper\Emailreport')->sendEmailReport(
$customEmailPath,
$senderInfo,
$receiverInfo,
$customerDetails = []
);