Get a list of skus in a category ID comma separated in Magento

GetSkusInCategory.php

<?php

require_once 'app/Mage.php';
umask(0);
Mage::app('default');

$cat_id = 2117;

$skus = array();

$category = Mage::getModel('catalog/category')->load($cat_id);
$collection = $category->getProductCollection()->addAttributeToSort('position');
Mage::getModel('catalog/layer')->prepareProductCollection($collection);

foreach ($collection as $product) {

	$product_id = $product->getId();
	$_product = Mage::getModel('catalog/product')->load($product_id);

	$skus[] = $_product->getSku();

}

$sku_list = implode(',', $skus);

echo $sku_list;

You should not run product model load inside a loop like this as it would cause performance issue.

Not sure if the SKU is already available inside the loop in your example without loading the model.

If not, try

 $collection = Mage::getModel('catalog/category')
                    ->load($categoryId)
                    ->getProductCollection();
// Run the foreach loop, the SKU should be available by using $product->getSku()

Can you write the same code for magneto 2 ?