Applying feedbacks - changing enable_history_search from an envvar to a configurable

IPython/terminal/interactiveshell.py

@@ -206,6 +206,10 b' class TerminalInteractiveShell(InteractiveShell):'
              "may be changed or removed in later releases."
     ).tag(config=True)
 
+    enable_history_search = Bool(True,
+        help="Allows to enable/disable the prompt toolkit history search"
+    ).tag(config=True)
+
     @observe('term_title')
     def init_term_title(self, change=None):
         # Enable or disable the terminal title.
@@ -269,11 +273,7 b' class TerminalInteractiveShell(InteractiveShell):'
                             history=history,
                             completer=IPythonPTCompleter(shell=self,
                                                     patch_stdout=patch_stdout),
-                            enable_history_search=(
-                                os.environ['enable_history_search'].capitalize()
-                                if 'enable_history_search' in os.environ
-                                else True
-                            ),
+                            enable_history_search=self.enable_history_search,
                             style=self.style,
                             mouse_support=self.mouse_support,
                             **self._layout_options()