Protect install target and add tests

install.sh

@@ -25,21 +25,38 @@ require_root() {
   fi
 }
 
+target_is_current_link() {
+  [[ -L ${TARGET_BIN} ]] || return 1
+  [[ $(readlink -- "${TARGET_BIN}") == "${SOURCE_SCRIPT}" ]]
+}
+
 install_link() {
   [[ -f ${SOURCE_SCRIPT} ]] || {
     printf '未找到入口脚本: %s\n' "${SOURCE_SCRIPT}" >&2
     exit 1
   }
   mkdir -p "$(dirname -- "${TARGET_BIN}")"
-  ln -sfn "${SOURCE_SCRIPT}" "${TARGET_BIN}"
+  if [[ -e ${TARGET_BIN} || -L ${TARGET_BIN} ]]; then
+    if target_is_current_link; then
+      chmod 755 "${SOURCE_SCRIPT}"
+      printf '链接已存在: %s -> %s\n' "${TARGET_BIN}" "${SOURCE_SCRIPT}"
+      return 0
+    fi
+    printf '目标已存在且不是当前脚本的链接，拒绝覆盖: %s\n' "${TARGET_BIN}" >&2
+    exit 1
+  fi
+  ln -s "${SOURCE_SCRIPT}" "${TARGET_BIN}"
   chmod 755 "${SOURCE_SCRIPT}"
   printf '已创建链接: %s -> %s\n' "${TARGET_BIN}" "${SOURCE_SCRIPT}"
 }
 
 uninstall_link() {
-  if [[ -L ${TARGET_BIN} || -e ${TARGET_BIN} ]]; then
+  if target_is_current_link; then
     rm -f "${TARGET_BIN}"
     printf '已删除链接: %s\n' "${TARGET_BIN}"
+  elif [[ -L ${TARGET_BIN} || -e ${TARGET_BIN} ]]; then
+    printf '目标不是当前脚本创建的链接，拒绝删除: %s\n' "${TARGET_BIN}" >&2
+    exit 1
   else
     printf '未发现已安装链接: %s\n' "${TARGET_BIN}"
   fi