check if a line is empty using bash

Question

I am trying to do a simple comparison to check if a line is empty using bash:

line=$(cat test.txt | grep mum )
if [ "$line" -eq "" ]
        then
        echo "mum is not there"
    fi

But it is not working, it says: [: too many arguments

Thanks a lot for your help!

Answer 1

You could also use the $? variable that is set to the return status of the command. So you'd have:

line=$(grep mum test.txt)
if [ $? -eq 1 ]
    then
    echo "mum is not there"
fi

For the grep command if there are any matches $? is set to 0 (exited cleanly) and if there are no matches $? is 1.