save log file for bash output

# Train and test the model
export CUDA_VISIBLE_DEVICES=2
dataset="xxx"
LOG="./caches/$dataset.txt.`date +'%Y-%m-%d_%H-%M-%S'`"
exec &> >(tee -a "$LOG")
echo Logging output to "$LOG"
echo 'Train the model ...'
python train.py --dataset $dataset