Warn if user executes !pip or !conda

Fixes  #12204

IPython/core/interactiveshell.py

@@ -2521,6 +2521,18 class InteractiveShell(SingletonConfigurable):
           Command to execute.
         """
         cmd = self.var_expand(cmd, depth=1)
+
+        # warn if there is an IPython magic alternative.
+        main_cmd = cmd.split()[0]
+        has_magic_alternatives = ("pip", "conda")
+        if main_cmd in has_magic_alternatives:
+            warnings.warn(
+                (
+                    "You executed the system command !{0} which may not work "
+                    "as expected. Try the IPython magic %{0} instead."
+                ).format(main_cmd)
+            )
+
         # protect os.system from UNC paths on Windows, which it can't handle:
         if sys.platform == 'win32':
             from IPython.utils._process_win32 import AvoidUNCPath