BLE gatttool interactive shell script - bash

Question

I established a connection with a BLE device using gatttool. First I connected to the device with sudo gatttool -t random -b FF:3C:8F:22:C9:C8 -I and connect. After that I read the value of specific characteristic with char-read-uuid 2d30c082-f39f-4ce6-923f-3484ea480596.
What I want to do is to automate the whole process and put the latter command (querying for value) in the loop, ideally saving each value (appending) to a text file. I tried something like
sudo gatttool -t random -b FF:3C:8F:22:C9:C8 -I <<EOF
connect
while[ 1 ]; do
char-read-uuid 2d30c082-f39f-4ce6-923f-3484ea480596 > output.txt
done
exit 1
EOF
but it does not help, since I am not even able to connect to the device (ideally there should be some delay between the first and the second command). Also after connecting, an interactive mode is enabled and the shell commands do not work there. I'd appreciate any clues on how to tackle this issue.

Answer 1

If gattool writes prompts to stdout (and doesn't suppress them given non-TTY file descriptors), consider something like:
#!/usr/bin/env bash
case $BASH_VERSION in ''|[123].*|4.0.*) echo "ERROR: bash 4.1 or newer required" >&2; exit 1;; esac
exec {output_fd}>output.txt
prompt_re='[>] '
capture_re='^handle:.*value:.*$'
wait_for_prompt() {
IFS= read -r line || return
while ! [[ $line =~ $prompt_re ]]; do
[[ $line =~ $capture_re ]] && printf '%s\n' "$line" >&$output_fd
IFS= read -r line || return
done
}
wait_for_prompt
echo connect
while wait_for_prompt; do
echo "char-read-uuid 2d30c082-f39f-4ce6-923f-3484ea480596"
done
...saved as yourscript, and invoked using socat as:
socat 'SYSTEM:sudo gatttool -t random -b FF:3C:8F:22:C9:C8 -I 2>&1' 'EXEC:./yourscript'
(assuming that sudo is configured to work without a TTY; otherwise, you might move it to be sudo socat).

Answer 2

Indeed, pexpect works fine here. You can find my solution below. The code reads the value of the specific UUID, which contains IMU readings (floats).
import pexpect
import struct
import time
import sys
IMU_MAC_ADDRESS = "FF:3C:8F:22:C9:C8"
UUID_DATA = "2d30c082-f39f-4ce6-923f-3484ea480596"
if __name__ == '__main__':
gatt = pexpect.spawn("gatttool -t random -b " + IMU_MAC_ADDRESS + " -I")
gatt.sendline("connect")
gatt.expect("Connection successful")
while(True):
gatt.sendline("char-read-uuid " + UUID_DATA)
gatt.expect("handle: 0x0011 value: ")
gatt.expect(" \r\n")
data = (gatt.before).decode('UTF-8').replace(" ", "").decode('hex')
print(struct.unpack('f', data)[0]