Replace all instances of a specific word and match original case

replace-cars-with-semi.txt

// Replace all instances of "car" with "semi" across entire website (case-preserving)
function replace_car_with_semi($content) {
    return preg_replace_callback('/\bcar\b/i', function($match) {
        // Preserve original case pattern
        if (ctype_upper($match[0])) {
            return 'SEMI';  // CAR -> SEMI
        } elseif (ctype_upper($match[0][0])) {
            return 'Semi';  // Car -> Semi
        }
        return 'semi';      // car -> semi
    }, $content);
}

// Apply to all major content areas
add_filter('the_content', 'replace_car_with_semi');      // Post content
add_filter('the_title', 'replace_car_with_semi');        // Post titles
add_filter('the_excerpt', 'replace_car_with_semi');      // Excerpts
add_filter('widget_text', 'replace_car_with_semi');      // Text widgets
add_filter('widget_title', 'replace_car_with_semi');     // Widget titles
add_filter('bloginfo', 'replace_car_with_semi');         // Site title/tagline
add_filter('wp_nav_menu_items', 'replace_car_with_semi'); // Menu items
add_filter('term_name', 'replace_car_with_semi');        // Category/tag names