diff --git a/src/colablinter/command.py b/src/colablinter/command.py
index a10f4d4..ad2c1e4 100644
--- a/src/colablinter/command.py
+++ b/src/colablinter/command.py
@@ -2,20 +2,49 @@
 
 from colablinter.logger import logger
 
-CELL_CHECK_COMMAND = (
-    "ruff check --select B,E,F,I,UP,SIM --ignore F401,E501 --stdin-filename=tmp.py"
-)
-CELL_CHECK_FIX_COMMAND = "ruff check --fix --select B,E,F,I,UP,SIM --ignore F401,E501 --stdin-filename=tmp.py"
-CELL_CHECK_UNSAFE_FIX_COMMAND = "ruff check --fix --select B,E,F,I,UP,SIM --ignore F401,E501 --stdin-filename=tmp.py --unsafe-fixes"
-CELL_FORMAT_COMMAND = "ruff format --stdin-filename=tmp.py"
+CELL_CHECK_COMMAND = [
+    "ruff",
+    "check",
+    "--select",
+    "B,E,F,I,UP,SIM",
+    "--ignore",
+    "F401,E501",
+    "--stdin-filename=tmp.py",
+]
+CELL_CHECK_FIX_COMMAND = [
+    "ruff",
+    "check",
+    "--fix",
+    "--select",
+    "B,E,F,I,UP,SIM",
+    "--ignore",
+    "F401,E501",
+    "--stdin-filename=tmp.py",
+]
+CELL_CHECK_UNSAFE_FIX_COMMAND = [
+    "ruff",
+    "check",
+    "--fix",
+    "--unsafe-fixes",
+    "--select",
+    "B,E,F,I,UP,SIM",
+    "--ignore",
+    "F401,E501",
+    "--stdin-filename=tmp.py",
+]
+CELL_FORMAT_COMMAND = [
+    "ruff",
+    "format",
+    "--stdin-filename=tmp.py",
+]
 
 
-def execute_command(command: str, input_data: str) -> str | None:
+def execute_command(command: list[str], input_data: str) -> str | None:
     try:
         result = subprocess.run(
             command,
             input=input_data,
-            shell=True,
+            shell=False,
             capture_output=True,
             text=True,
             encoding="utf-8",
diff --git a/src/colablinter/magics.py b/src/colablinter/magics.py
index fa2f0d1..9874fb8 100644
--- a/src/colablinter/magics.py
+++ b/src/colablinter/magics.py
@@ -29,7 +29,7 @@ def clcheck(self, line: str, cell: str) -> None:
     @cell_magic
     def clunsafefix(self, line: str, cell: str) -> None:
         if self.shell is None:
-            raise Exception
+            raise RuntimeError("IPython shell is not initialized.")
 
         stripped_cell = cell.strip()
         fixed_code = cell_check_unsafe_fix(stripped_cell)
@@ -54,6 +54,9 @@ def clautofix(self, line: str) -> None:
             logger.info("Usage: %clautofix on or %clautofix off.")
 
     def __execute(self, cell: str) -> None:
+        if self.shell is None:
+            raise RuntimeError("IPython shell is not initialized.")
+
         if self._is_autofix_active:
             logger.info(
                 "autofix is temporarily suppressed to prevent dual execution. "
@@ -62,8 +65,6 @@ def __execute(self, cell: str) -> None:
             self.__unregister()
 
         try:
-            if self.shell is None:
-                raise Exception
             self.shell.run_cell(cell, silent=False, store_history=True)
         except Exception as e:
             logger.exception(f"Code execution failed: {e}")