Use WordPress Path and URL Functions — Never Hardcode

// ❌ Hardcoded domain — breaks on staging, local dev, and domain changes
$logo = 'https://example.com/wp-content/themes/my-theme/images/logo.png';
$ajax = 'https://example.com/wp-admin/admin-ajax.php';
$home = 'https://example.com/';
 
// ❌ Hardcoded filesystem path — breaks on different servers
require_once '/var/www/html/wp-content/plugins/my-plugin/includes/helpers.php';
$upload_path = '/var/www/html/wp-content/uploads/';
 
// ❌ Assuming wp-content is in the default location
$plugin_url = get_site_url() . '/wp-content/plugins/my-plugin/assets/style.css';
// Breaks if WP_CONTENT_DIR is customized

// ✅ Theme URLs and paths
$logo = get_template_directory_uri() . '/images/logo.png';          // Parent theme URL
$logo = get_stylesheet_directory_uri() . '/images/logo.png';       // Child theme URL
$path = get_template_directory() . '/includes/helpers.php';         // Parent theme filesystem
$path = get_stylesheet_directory() . '/includes/helpers.php';       // Child theme filesystem
 
// ✅ Plugin URLs and paths
$asset_url  = plugin_dir_url( __FILE__ ) . 'assets/style.css';     // Plugin asset URL
$asset_url  = plugins_url( 'assets/style.css', __FILE__ );         // Same, different syntax
$plugin_dir = plugin_dir_path( __FILE__ );                          // Plugin filesystem path (trailing /)
require_once plugin_dir_path( __FILE__ ) . 'includes/helpers.php';
 
// ✅ Site URLs
$home     = home_url( '/' );                    // Frontend homepage
$site     = site_url( '/wp-login.php' );        // WordPress install URL
$admin    = admin_url( 'admin-ajax.php' );      // Admin URL
$ajax_url = admin_url( 'admin-ajax.php' );      // Correct AJAX endpoint
 
// ✅ Upload directory
$upload_dir = wp_upload_dir();
$base_path  = $upload_dir['basedir'];  // /var/www/html/wp-content/uploads
$base_url   = $upload_dir['baseurl'];  // https://example.com/wp-content/uploads
 
// ✅ WordPress core paths
$abspath       = ABSPATH;                    // WordPress root
$content_dir   = WP_CONTENT_DIR;             // wp-content filesystem path
$content_url   = content_url();              // wp-content URL
$includes_dir  = ABSPATH . WPINC . '/';      // wp-includes filesystem path

# Find hardcoded domain URLs to wp-content
grep -rn "https\?://.*wp-content" wp-content/plugins/ wp-content/themes/ --include="*.php"
# Find hardcoded filesystem paths
grep -rn "/var/www\|/home/[a-z]" wp-content/plugins/ wp-content/themes/ --include="*.php"