Parsing iw wlan0 scan output

Question

I wrote wlan manager script to handle open/ad-hoc/wep/wpa2 networks. Now im trying to parse iw wlan0 scan output to get nice scan feature to my script. My goal is to get output like this :

SSID        channel     signal      encryption
wlan-ap     6           70%         wpa2-psk
test        1           55%         wep

What i have achived already is output like this :

$ iw wlan0 scan | grep 'SSID\|freq\|signal\|capability' | tac
SSID: Koti783
signal: -82.00 dBm
capability: ESS Privacy ShortPreamble SpectrumMgmt ShortSlotTime (0x0531)
freq: 2437

I have been trying to study bash/sed/awk but havent found yet a way to achieve what im trying. So what is good way to achieve that?

Answer 1

Here is a simple Bash function which uses exclusively Bash internals and spawns only one sub-shell:

#!/bin/bash 
function iwScan() {
   # disable globbing to avoid surprises
   set -o noglob
   # make temporary variables local to our function
   local AP S
   # read stdin of the function into AP variable
   while read -r AP; do
     ## print lines only containing needed fields
     [[ "${AP//'SSID: '*}" == '' ]] && printf '%b' "${AP/'SSID: '}\n"
     [[ "${AP//'signal: '*}" == '' ]] && ( S=( ${AP/'signal: '} ); printf '%b' "${S[0]},";)
   done
   set +o noglob
}

iwScan <<< "$(iw wlan0 scan)"

Output:

-66.00,FRITZ!Box 7312
-56.00,ALICE-WLAN01
-78.00,o2-WLAN93
-78.00,EasyBox-7A2302
-62.00,dlink
-74.00,EasyBox-59DF56
-76.00,BELAYS_Network
-82.00,o2-WLAN20
-82.00,BPPvM

The function can be easily modified to provide additional fields by adding a necessary filter into the while read -r AP while-loop, eg:

[[ "${AP//'last seen: '*}" == '' ]] && ( S=( ${AP/'last seen: '} ); printf '%b' "${S[0]},";)

Output:

-64.00,1000,FRITZ!Box 7312
-54.00,492,ALICE-WLAN01
-76.00,2588,o2-WLAN93
-78.00,652,LN8-Gast
-72.00,2916,WHITE-BOX
-66.00,288,ALICE-WLAN
-78.00,800,EasyBox-59DF56
-80.00,720,EasyBox-7A2302
-84.00,596,ALICE-WLAN08

Answer 2

it's generally bad practice to try parsing complex output of programs intended for humans to read (rather than machines to parse).

e.g. the output of iw might change depending on the language settings of the system and/or the version of iw, leaving you with a "manager" that only works on your development machine.

instead you might use the same interface that iw uses to get it's information: the library backend libnl

you might also want to have a look at the wireless-tools (iwconfig, iwlist,...) that use the libiw library.