If telnet output contains something execute action - bash

Question

I am trying to write a small script in bash. My target is that a Phone Call on my FritzBox will mute or pause my TV.
I get the information of a call via telnet (telnet fritz.box 1012) on my RaspberryPi and if there is coming a phone call in I get this output:
24.08.15 14:03:05;RING;0;017mobilephonenumber;49304myhomenumber;SIP0;
The only Part that is every time the same is the RING before the calling number. What I need is a script that checks the output of the telnet and if in the telnet output is a ring than execute an action in my case i just need to do a http request on an internal site or start another script.
This is what I have tried is this:
#!/bin/bash
#string='echo "My string"'
string=$(telnet –e p fritz.box 1012)
for reqsubstr in 'alt' 'RING';do
if [ -z "${string##*$reqsubstr*}" ] ;then
echo "String '$string' contain substring: '$reqsubstr'."
else
echo "String '$string' don't contain substring: '$reqsubstr'."
fi
done
But I don`t get the output of my telnet session into the string. Anyone who can help me?

Answer 1

After you latest comment, and reading your question again, I think we can go for something simpler based on nc (netcat).
Let assume we create a bash script called action.sh
#!/bin/bash
while true;
do
read logline
for substr in 'alt' '\;RING\;'
do
if [[ "$logline" = *${substr}* ]]; then
echo "Got a match"
fi
done
done
Make the script executable, chmod +x action.sh, then start it with nc as follow:
nc -l fritz.box 1012 | ./action.sh
It will listen infinitely for incoming traffic from the box and should act as you want. I don't have your box obviously and I tested by starting it as nc -l 127.0.0.1 12000 and then provided input via telnet 127.0.0.1 12000, providing your RING sample. It seems to work.
$ nc -l 127.0.0.1 12000 | ./action.sh
Got a match
017mobilephonenumber
Got a match
017mobilephonenumber
Would this be more acceptable to you ? without expect (I am not an expect wizard anyway).
I hope this answer will help you more.

Answer 2

do you have access to expect? It is meant exactly for such kind of scenario. man expect is your friend, and I found a fair tutorial via google. If you google for modem expect you can find sample script for such scenario (I can find some for FritzBox too but not sure it's the same box as yours). I haven't used it in ages, though.

Answer 3

Here my short conclusion:
To see incomming calls on your FritzBox you can simply execute:
telnet fritz.box 1012
in your terminal.
The output should look like that:
24.08.15 14:03:05;RING;0;017mobilephonenumber;49304myhomenumber;SIP0;
I my case I want the execute an command the mutes my TV.
Here are the instructions how I controll my TV via Web/RaspberryPi (Philips Harmony Hub) if some one is interested.
To execute a command on an incomming call create a script called action.sh
#!/bin/bash
while true;
do
read logline
for substr in 'alt' '\;RING\;'
do
if [[ "$logline" = *${substr}* ]]; then
echo "Got a match"
#here you can put the command you want to execute on an incoming call
fi
done
done
After you create it make it executable using chmod +x action.sh
After that you can start the script using nc 192.168.1.1 1012 | action.sh
And that's how you execute a script on an incomming call!
Special thanks to tgo!!