There are several commands, some more detailed than others, for scanning the wireless spectrum from the terminal on your Raspberry Pi.
The first command I recommend shows details of all the wireless networks detected by your network adapter:
sudo iw dev wlan0 scan
if you want to scan a specific channel, you can use the following command:
sudo iw dev wlan0 scan freq 2412
where 2412 indicates the frequency 2.412 GHz (channel 1); the frequency must be entered without the decimal point.
To view the various channels and frequencies supported by your device, you can use the following command:
sudo iwlist wlan0 channel
and the result will be similar to the following:
wlan0 32 channels in total; available frequencies :
Channel 01 : 2.412 GHz
Channel 02 : 2.417 GHz
Channel 03 : 2.422 GHz
Channel 04 : 2.427 GHz
Channel 05 : 2.432 GHz
Channel 06 : 2.437 GHz
Channel 07 : 2.442 GHz
Channel 08 : 2.447 GHz
Channel 09 : 2.452 GHz
Channel 10 : 2.457 GHz
Channel 11 : 2.462 GHz
Channel 12 : 2.467 GHz
Channel 13 : 2.472 GHz
Channel 36 : 5.18 GHz
Channel 40 : 5.2 GHz
Channel 44 : 5.22 GHz
Channel 48 : 5.24 GHz
Channel 52 : 5.26 GHz
Channel 56 : 5.28 GHz
Channel 60 : 5.3 GHz
Channel 64 : 5.32 GHz
Channel 100 : 5.5 GHz
Channel 104 : 5.52 GHz
Channel 108 : 5.54 GHz
Channel 112 : 5.56 GHz
Channel 116 : 5.58 GHz
Channel 120 : 5.6 GHz
Channel 124 : 5.62 GHz
Channel 128 : 5.64 GHz
Channel 132 : 5.66 GHz
Channel 136 : 5.68 GHz
Channel 140 : 5.7 GHz
Current Frequency:2.432 GHz (Channel 5)
As you can see, the last line shows the channel currently used by the network you are connected to.
If instead you want to see a list of the wireless networks detected by your Raspberry Pi, you can use the following command:
sudo iw dev wlan0 scan | grep SSID | sort | uniq -c | sort -n
Enjoy!
