How can I “Open an app from an unidentified developer” without using the GUI?

macos command-line gatekeeper

Solution 1:

You'll either have to change the settings under System Preferences > Security & Privacy > General > Allow applications downloaded from: to Anywhere or in a Terminal, strip the xattr com.apple.quarantine attribute from the downloaded file(s).

xattr -dr com.apple.quarantine "unidentified_thirdparty.app"

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