This snippet code is to show gist snippet into the WordPress content with just pasting the URL into post content

gist-wp-embed-url

wp_embed_register_handler( 'gist', '#https://gist\.github\.com/(.+?)/(.+?)($|&)#i', 'wp_embed_handler_gist' );

function wp_embed_handler_gist( $matches, $attr, $url, $rawattr ) {

    $embed = sprintf(
            '<script src="https://gist.github.com/%1$s/%2$s.js"></script>',
            esc_attr($matches[1]),
            esc_attr($matches[2])
            );

    return apply_filters( 'embed_gist', $embed, $matches, $attr, $url, $rawattr );
}