Mac Technique: How to Enable the Hidden Security & Privacy Option to Allow Apps from Unidentified Developers

With macOS High Sierra 10.13.4, there is no option by default to allow apps from unidentified developers in  -> System Preferences -> Security & Privacy -> General:

Close the window and type the following command in terminal:

sudo spctl --master-disable

and enter your password. Now go back to and the previously hidden Anywhere option is displayed:

Note that if you change a more secure option, the Anywhere option is hidden again when you turn on the Security & Privacy window next time.