diff --git a/src/utility.sh b/src/utility.sh
index 99746a7..dacb48a 100644
--- a/src/utility.sh
+++ b/src/utility.sh
@@ -16,9 +16,21 @@ log() {
 set_opts() {
   sign="$1"
 
-  set "${sign}o" errexit
-  set "${sign}o" nounset
-  set "${sign}o" pipefail
+  set_opt() {
+    local opt="$1"
+
+    if set -o | grep -q "^$opt[[:space:]]"; then
+      set "${sign}o" "$opt"
+      log debug "[set_opts] Set: $(set -o | grep -q "^$opt[[:space:]]")"
+    else
+      log fatal "Unsupported shell: no $opt option support"
+      return 1
+    fi
+  }
+
+  set_opt errexit
+  set_opt nounset
+  set_opt pipefail
 }
 
 prepare_directories() {
diff --git a/tori b/tori
index 261c82b..29a5efd 100755
--- a/tori
+++ b/tori
@@ -2,17 +2,13 @@
 
 main() {
   # paths
-  VERSION="0.4.1 2024-07-14"
+  VERSION="0.5.0 2024-07-18"
   TORI_ROOT="$HOME/.local/share/tori"
   CONFIG_ROOT="$HOME/.config/tori"
   TMP_DIR="/tmp/tori"
   CACHE_DIR="$HOME/.cache/tori"
 
-  check_core_paths
-
-  . "$TORI_ROOT/src/index.sh"
-
-  # state
+  # os-independent state
 
   DEBUG=$DEBUG
 
@@ -20,13 +16,16 @@ main() {
   argument="$1"
   parameter="$2"
 
+  # import source
+
+  check_core_paths
+  . "$TORI_ROOT/src/index.sh"
   set_opts -
 
-  ## global constants
+  ## os-dependent state
   OS="$(get_operating_system)"
   PACKAGE_CACHE="$CACHE_DIR/${OS}_packages.cache"
 
-  ## global state
   base_files=
   bkp_files=
   user_packages=