###script that works###
while [ ! -f "Test.FChk" ]
do
    echo "Checking job status of Gaussian: $JOBNAME..."
    sleep 5
done

###script that doesnt work###
while true; do
    if [[ ! -f "Test.FChk" && -f "run.log" ]]; then
        echo "Checking job status..."
        sleep 5
        printf "Calculation failed, script ended"
        return
    fi
    break
done