From ArchWiki

I have made some modifications to this script to better suit roaming in networks with multiple APs and same ESSID. I'll post my version here, perhaps it will be of use for someone.

Quick explanation of changes: aKNOWNNETS is read straight from filenames in network-profiles, no need to edit multiple files when adding new networks. Changed netdetect to identify networks by ESSID instead of MAC.

To /etc/rc.conf:

  aKNOWNNETS=`ls /etc/network-profiles`
  NET_PROFILES=(detect)

To /usb/bin/netdetect

1. !/bin/bash

  . /etc/rc.conf
  aSCANNEDNETS=(`ifconfig wlan0 up; iwlist wlan0 scanning | grep ESSID | tr \" \  | awk '{print $2}'`)
  for J in ${aSCANNEDNETS[*]} ; do
       for K in ${aKNOWNNETS[*]} ; do
               if [ $J == $K ]
               then
                       DET_ESSID=$K
                       break
               fi
       done
       if [ $DET_ESSID ]
       then
               break
       fi
  done
  if [ $DET_ESSID ]
  then
       netcfg $DET_ESSID
  else
       echo "could not detect a known AP..."
       netcfg -c lan-dhcp
  fi