Automatic Wi-Fi the Debian-way

interfaces

auto wlan0
mapping wlan0
	script /usr/local/sbin/wlan-detect.sh
	map HomeAP wlan0-home
	map OfficeAP wlan0-office

iface wlan0-home inet dhcp
	wpa-ssid HomeAP
	wpa-psk HomeAccessPointPassphrase
	wpa-key-mgmt WPA-PSK
	wpa-pairwise TKIP CCMP
	wpa-group TKIP CCMP
	wpa-proto WPA RSN

iface wlan0-office inet dhcp
	wpa-ssid OfficeAP
	wpa-psk OfficeAccessPointPassphrase
	wpa-key-mgmt WPA-PSK
	wpa-pairwise TKIP CCMP
	wpa-group TKIP CCMP
	wpa-proto WPA RSN

wlan-detect.sh

#!/bin/sh
# Script for automatic mapping wireless network interface to available and known
# access point. For more details see interfaces(5) mapping options. Example
# interfaces(5) file is provided.
#
# Note that access point ESSID and first argument in ``map'' directive should
# match.

IFACE="$1"
CTRL_SOCKET="/var/run/wpa_supplicant"

# We cannot perform AP scanning until interface is down. Bring up wlan interface
# with wpa_supplicant and wait a little.
wpa_supplicant -i $IFACE -C $CTRL_SOCKET &
PID=$!
sleep 5

SCAN_RESULT=`mktemp`
iwlist $IFACE scan > $SCAN_RESULT

# Simple check of scanning results. Script stops searching when first AP is
# found.
while read SSID IFACE_ALIAS ; do
	if ( grep "ESSID:\"$SSID\"" $SCAN_RESULT > /dev/null ) ; then
		echo $IFACE_ALIAS
		break
	fi
done

# Come cleanup before exit.
kill $PID
rm $SCAN_RESULT

exit 0