Hcitool lescan will not print in real time to a file

Question

UPDATE: I solved my solution using os.system:

sensortag=0
while sensortag != "B4:99:4C:64:33:E0":
    #call the command and write to scan.txt file and then fill the process.
    #loop to find if the MAC address given is available
    os.system("hcitool lescan> scan.txt & pkill --signal SIGINT hcitool")
    scan = open("scan.txt","r")
    readscan = scan.read()
    if "B4:99:4C:64:33:E0" in readscan:
        print "SensorTag found."
        sensortag = "B4:99:4C:64:33:E0"

I have two programs, essentially the same, but with two different commands, on a Raspberry PI, running Raspbian.

What I am trying to do is write both command outputs to a file, so I can process them later on.

I am puzzled to why the first program won't work, yet the second one will.

The First program has a "sudo timeout 5 hcitool lescan" command, which does not work.

import os
import subprocess

#r+ because the file is already there, w without the file
myfile = open("scan.txt", "r+")

#Reset Bluetooth interface, hci0
os.system("sudo hciconfig hci0 down")
os.system("sudo hciconfig hci0 up")

#Scan for bluetooth devices
dev = subprocess.Popen(["sudo timeout 5 hcitool lescan"], stdout=subprocess.PIPE, shell=True)
(device, err) = dev.communicate()

#Print bluetooth devices
print device

#Write the hcitool lescan output to a file
myfile.write(device)

#Close the file
myfile.close()

Here is the Second program I have which works fine printing the "sudo hciconfig":

import os
import subprocess

#r+ because the file is already there, w without the file
myfile = open("test.txt", "r+")

#Reset Bluetooth interface, hci0
os.system("sudo hciconfig hci0 down")
os.system("sudo hciconfig hci0 up")

#Make sure device is up
interface = subprocess.Popen(["sudo hciconfig"], stdout=subprocess.PIPE, shell=True)
(int, err) = interface.communicate()

#Print hciconfig to make sure it's up
print int

#Write the hciconfig output to a file
myfile.write(int)

#Close the file
myfile.close()

Answer 1

I solved my solution using os.system and killing the scan straight away:

sensortag=0
while sensortag != "B4:99:4C:64:33:E0":
    #call the command and write to scan.txt file and then fill the process.
    #loop to find if the MAC address given is available
    os.system("hcitool lescan> scan.txt & pkill --signal SIGINT hcitool")
    scan = open("scan.txt","r")
    readscan = scan.read()
    if "B4:99:4C:64:33:E0" in readscan:
        print "SensorTag found."
        sensortag = "B4:99:4C:64:33:E0"

Answer 2

Using terminal only, following command did work:

hcitool lescan > scan.txt & sleep 2 && pkill --signal SIGINT hcito

I will just leave it here, maybe this will help someone.

Answer 3

After spending a few hours working this out, I came up with this solution. The problem with hcitool lescan is that it doesn't return until it receives a SIGINT, so we send it one with Python:

    bashCommand = "hcitool lescan"
    process = subprocess.Popen(bashCommand.split(), stdout=subprocess.PIPE)
    time.sleep(3)
    os.kill(process.pid, signal.SIGINT)
    output = process.communicate()[0]

This for me returned a string containing all of the mac addresses found, after a 3 second search.