Format products and variations SKU on woocommerce wordpress product page

Question

I want to show only the first 5 digits of the composed SKU for products, here's the context:

Main product SKU: 12345 Variation SKU: 67890

SKU showed on product page: 12345-67890

I want to show only the first (main product) SKU number:

this is what I tried:

$sku = $product->get_sku();
$skunodash = substr($sku, 0, 5);
        
<span class="sku_wrapper"><?php esc_html_e( 'SKU :', 'woocommerce' ); ?> <span class="sku"><?php echo $skunodash ? $sku: esc_html__( 'N/A', 'woocommerce' ); ?></span></span>

I have also tried:

$skunodash = explode("-", $sku)

But nothing works, and just shows the whole SKU no matter what.

What am I doing wrong?

Thans in advance.