Index: lldb/source/Commands/CommandObjectSettings.cpp
===================================================================
--- lldb/source/Commands/CommandObjectSettings.cpp
+++ lldb/source/Commands/CommandObjectSettings.cpp
@@ -102,6 +102,9 @@
       case 'g':
         m_global = true;
         break;
+      case 'e':
+        m_exists = true;
+        break;
       default:
         llvm_unreachable("Unimplemented option");
       }
@@ -112,6 +115,7 @@
     void OptionParsingStarting(ExecutionContext *execution_context) override {
       m_global = false;
       m_force = false;
+      m_exists = false;
     }
 
     llvm::ArrayRef<OptionDefinition> GetDefinitions() override {
@@ -120,7 +124,8 @@
 
     // Instance variables to hold the values for command options.
     bool m_global = false;
-    bool m_force;
+    bool m_force = false;
+    bool m_exists = false;
   };
 
   void
@@ -219,13 +224,12 @@
                                              var_name, var_value);
     }
 
-    if (error.Fail()) {
+    if (error.Fail() && !m_options.m_exists) {
       result.AppendError(error.AsCString());
       return false;
-    } else {
-      result.SetStatus(eReturnStatusSuccessFinishResult);
     }
 
+    result.SetStatus(eReturnStatusSuccessFinishResult);
     return result.Succeeded();
   }
 
Index: lldb/source/Commands/Options.td
===================================================================
--- lldb/source/Commands/Options.td
+++ lldb/source/Commands/Options.td
@@ -22,6 +22,8 @@
     Desc<"Apply the new value to the global default value.">;
   def setset_force : Option<"force", "f">,
     Desc<"Force an empty value to be accepted as the default.">;
+  def setset_exists : Option<"exists", "e">,
+    Desc<"Only set the setting if it exists. Don't print an error otherwise.">;
 }
 
 let Command = "settings write" in {
Index: lldb/test/API/commands/settings/TestSettings.py
===================================================================
--- lldb/test/API/commands/settings/TestSettings.py
+++ lldb/test/API/commands/settings/TestSettings.py
@@ -779,3 +779,13 @@
         # finally, confirm that trying to set a setting that does not exist still fails.
         # (SHOWING a setting that does not exist does not currently yield an error.)
         self.expect('settings set target.setting-which-does-not-exist true', error=True)
+
+    def test_settings_set_exists(self):
+        cmdinterp = self.dbg.GetCommandInterpreter()
+
+        # An unknown option should succeed.
+        self.expect('settings set -e foo bar')
+        self.expect('settings set --exists foo bar')
+
+        # A known option should fail if its argument is invalid.
+        self.expect("settings set auto-confirm bogus", error=True)