How do I confirm WiFi connection status in Linux?

The iw tool can be used to read the status of the device:

# iw dev

        Unnamed/non-netdev interface
                wdev 0x2
                addr 7e:4a:78:cc:85:77
                type P2P-device
                txpower 31.00 dBm
        Interface wlan0
                ifindex 7
                wdev 0x1
                addr aa:bb:cc:07:0c:b1
                ssid testAP
                type AP
                channel 11 (2462 MHz), width: 20 MHz, center1: 2462 MHz
                txpower 31.00 dBm

Managed/client mode link information:

# iw wlan0 link

Connected to aa:bb:cc:12:34:56 (on wlan0)
        SSID: testAP
        freq: 2462
        RX: 364 bytes (2 packets)
        TX: 3782 bytes (22 packets)
        signal: -31 dBm
        tx bitrate: 2.0 MBit/s
        bss flags:      short-slot-time
        dtim period:    2
        beacon int:     200

AP mode to read connected client information:

# iw wlan0 station dump

Station aa:bb:cc:8b:6c:fe (on wlan0)
        inactive time:  3000 ms
        rx bytes:       6479
        rx packets:     37
        tx bytes:       9706
        tx packets:     66
        tx failed:      0
        signal:         -44 [-44] dBm
        tx bitrate:     1.0 MBit/s
        rx bitrate:     65.0 MBit/s
        authorized:     yes
        authenticated:  yes
        associated:     yes
        WMM/WME:        yes
        TDLS peer:      no
        DTIM period:    2
        beacon interval:100
        short slot time:yes
        connected time: 20 seconds