Add missing import

Author: gjbex

hands-on/shell_interaction.ipynb

@@ -51,6 +51,15 @@
     "sh.ls('-l')"
    ]
   },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "!ls -l"
+   ]
+  },
   {
    "cell_type": "code",
    "execution_count": null,
@@ -611,6 +620,15 @@
     "If you need to add or modify environment variables, it is good practice to do that on a copy of `os.environ`."
    ]
   },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "import os"
+   ]
+  },
   {
    "cell_type": "code",
    "execution_count": null,