-

root@portaptty:~# iwlist wlan0 scan | awk -F: '/Freq/ { print $2}' | sort -nr | uniq -c
      1 5.825 GHz
      1 5.805 GHz
      3 5.785 GHz
      3 5.765 GHz
      1 5.745 GHz
      1 5.24 GHz (Channel 48)
      2 5.22 GHz (Channel 44)
      1 5.2 GHz (Channel 40)
      2 5.18 GHz (Channel 36)
     18 2.462 GHz (Channel 11)
      1 2.457 GHz (Channel 10)
      5 2.452 GHz (Channel 9)
     12 2.447 GHz (Channel 8)
      1 2.442 GHz (Channel 7)
     11 2.437 GHz (Channel 6)
      3 2.432 GHz (Channel 5)
      1 2.417 GHz (Channel 2)
     17 2.412 GHz (Channel 1)