Change woocommerce add to cart text

add_to_cart_button_text.php

<?php
/**
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 Change woocommerce add to cart text
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*/

add_filter( 'woocommerce_product_single_add_to_cart_text' , 'woo_custom_cart_button_text' );

function woo_custom_cart_button_text() {
return __('Buy Now!' , 'woocommerce');
}

add_filter( 'woocommerce_product_add_to_cart_text', 'woocommerce_shop_page_add_to_cart_callback' );  
function woocommerce_shop_page_add_to_cart_callback() {
    return __( 'Buy Now', 'woocommerce' );
}