wpa_supplicant

scan

scan_results

add_network

set_network 0 ssid "MYSSID"

set_network 0 psk "passphrase"

OR > set_network 0 key_mgmt NONE

enable_network 0

save_config

might want to 'sudo sv restart dhcpcd'

CLI

You can use all commands non-interactively, from the cli, e.g.:

wpa_cli scan

wpa_cli scan_results

But remember to escape the quotes, so adding a network would be:

wpa_cli set_network 3 psk ""passphrase""