diff --git a/update.sh b/update.sh
index 062c2c9..111f595 100755
--- a/update.sh
+++ b/update.sh
@@ -150,6 +150,16 @@ refresh_brew_metadata() {
 	brew_metadata_refreshed=1
 }
 
+# 输出过期包列表：brew outdated 发现过期包时退出码为 1，只有无输出且非零才视为查询失败。
+brew_outdated() {
+	brew_outdated_output=$(brew outdated "$@")
+	brew_outdated_status=$?
+	if [ "$brew_outdated_status" -ne 0 ] && [ -z "$brew_outdated_output" ]; then
+		return 1
+	fi
+	printf '%s\n' "$brew_outdated_output"
+}
+
 update_brew_formula_if_installed() {
 	formula=$1
 	description=$2
@@ -159,7 +169,7 @@ update_brew_formula_if_installed() {
 			record_update_failure "$description"
 			return 0
 		}
-		outdated_formula=$(brew outdated --formula --quiet "$formula") || {
+		outdated_formula=$(brew_outdated --formula --quiet "$formula") || {
 			record_update_failure "$description"
 			return 0
 		}
@@ -213,7 +223,7 @@ update_kitty() {
 
 	if command -v brew >/dev/null 2>&1 && brew list --cask kitty >/dev/null 2>&1; then
 		if refresh_brew_metadata; then
-			if outdated_kitty=$(brew outdated --cask --quiet kitty); then
+			if outdated_kitty=$(brew_outdated --cask --quiet kitty); then
 				if [ -z "$outdated_kitty" ]; then
 					say "✓ Kitty 已是最新版本。"
 				else