Check for I2C device presence

Question

I'm using I2Ctools to read data off of some devices attached to a raspberry pi via the I2C interface. I want to check if a device in a certain address is present or not. If present, read the data from it. If not, read data off another device.

Right now if the device is not present, I'm checking for an error string "Error: Read failed". I don't think this is the most robust way of doing this, so I was hoping someone might point something out.

I'm limited to using shell scripts.

EDIT: To clarify, I'm using i2cget on a particular address and storing the value in a variable. If the value is literally "Error: Read failed", I know that the device is not present and so move on from there.

Answer 1

No doubt there's some awk/sed wizard around who can do this in one line, but shell clutz that I am:

#!/bin/bash

bus=1
if [[ -n $2 ]]; then
    bus=$2
fi

mapfile -t data < <(i2cdetect -y $bus)

for i in $(seq 1 ${#data[@]}); do
    line=(${data[$i]})
    echo ${line[@]:1} | grep -q $1
    if [ $? -eq 0 ]; then
        echo "$1 is present."
        exit 0
    fi
done

echo "Not found."
exit 1  

Takes one or two arguments. The first is the 2 digit hexadecimal address you are looking for, and the second is the i2c-dev bus number (defaults to 1).

Remember, running i2cdetect has some warnings attached to it. I'm actually not sure how seriously they apply on the pi though.