To resolve this :
f [[ -f /var/log/deploy.log ]] && [[ ! -h /var/log/deploy.log ]]; then
mv /var/log/deploy.log /var/log/deploy-old.log
fi
exec > >(tee -a "/var/log/deploy-$log_timestamp.log") 2>&1
ln -sfT "deploy-$log_timestamp.log" /var/log/deploy.log