update post meta

gistfile1.php

<?php
function save_urun_meta_price( $post_id ) {


    // - Update the post's metadata.

    if ( isset( $_REQUEST['urun_indirimli_fiyat'] ) ) {
        $product_price = get_post_meta( $post_id, 'urun_fiyat', true );
        $product_discount = of_get_option('urun_discount');

            $yuzde =  ($product_discount / 100)*$product_price;
            $discounted = $product_price-$yuzde;

        update_post_meta( $post_id, 'urun_indirimli_fiyat', $discounted  );
    }

}
add_action( 'save_post', 'save_urun_meta_price' );