Check for successful connection using rfcomm

Question

I am trying to connect my phone to my RaspberryPi using a blue tooth dongle (not trying to do anything earth shattering, just determine when my phone is in the area). If I turn my phone's blue tooth on and issue the following command, I get the following output (before anyone starts preaching to me about how this is a breach of security, let me remind you that that is not my actual phone bluetooth id):

command:

sudo rfcomm connect 0 AA:BB:CC:DD:EE:FF 10
echo $?

output:

Connected /dev/rfcomm0 to AA:BB:CC:DD:EE:FF on channel 10
Press CTRL-C for hangup
0

Now if I turn my phone's bluetooth off, and issue the same command, I get the following output (again, all id's have been changed to protect the innocent).

command:

sudo rfcomm connect 0 AA:BB:CC:DD:EE:FF 10
echo $?

output:

Can't connect RFCOMM socket: Host is down
0

Since I am trying to determine when the phone is in the room and when it leaves, I need some way (some other way) of detecting when the dongle can and can not connect to it. How can I go about achieving this? (NOTE: I tried removing the phone from the building and even turning it off completely)

EDIT: I have considered catching the stderr message and testing it like so

error=$`sudo rfcomm connect 0 AA:BB:CC:DD:EE:FF 10 >/dev/null` &
if [ $error=="Can't connect RFCOMM socket: Host is down" ]
then
    ...
fi;

But the problem is that rfcomm has to run in the background.

Answer 1

I have not quite figured out how to do this, but this is how I got around it. I simply wait 5 seconds after the sudo rfcomm connect 0 AA:BB:CC:DD:EE:FF 10 command, and then I check to see if there is a connection. I suspect that this actually works perfectly, as the next iteration will catch any mistakes made, but don't quote me on it. Perhaps a more experience . I have included the minimal working example (MWE) so you can follow it.

MWE:

#!/bin/bash

phone1="AA:BB:CC:DD:EE:FF" #Address of phone
inside=1  # Whether the phone is 'inside' the house (0) or 'outside (1)

phoneDetected ()
{
   # Search for phone
   hcitool rssi $phone1 &>/dev/null
   ret=$?

   # If search was unsuccessful,
   if [ $ret -ne 0 ]
   then
      # Add phone
      sudo rfcomm connect 0 $phone1 10 &>/dev/null &

      # Note: the return code of rfcomm will almost always be 0,
      # so don't rely on it if you are looking for failed connections,
      # instead wait 5 seconds for rfcomm to connect, then check
      # connection again. Note this is not fool proof as an rfcomm
      # command taking longer than 5 seconds could break this program,
      # however, it generally only takes 2 seconds.
      sleep 5
      hcitool rssi $phone1 &>/dev/null
      ret=$?
   fi;

   # Case 1) we are now connected (ret=0) and we were previously outside (inside=1)
   if [ $ret -eq 0 ] && [ $inside -eq 1 ]
   then
      # change state to inside and do something (I am playing a song)
      inside=0
      mplayer /home/pi/documents/rasbpi/raspi1/media/audio/1.mp3 &>/dev/null
   # Case 2) we are no longer connected (ret=1) but we were previously inside (inside=0)
   elif [ $ret -eq 1 ] && [ $inside -eq 0 ]
   then
      # change state to outside and do something (I am playing another song)
      inside=1
      mplayer /home/pi/documents/rasbpi/raspi1/media/audio/2.mp3 &>/dev/null
   fi;
}

# run an infinite loop
while :
do
   phoneDetected $phone1
done