ssh-add(1) on macOS
The text 8e1271f1edb9, as macOS 10.13.1, macOS 10.13, macOS 10.12.6, macOS 10.12.5, macOS 10.12.4, macOS 10.12.3, macOS 10.12.2 shipped it.
adds private key identities to the authentication agent
Flags it lists
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-c -
-d -
-e -
-k -
-l -
-s -
-t -
-x