crontab every 2 two
#crontab -e
30 20 8-14,22-28 * * test $(date +%u) -eq 1 && /usr/local/bin/backup.sh >> /var/log/backup.log 2>&1
date +%u ：顯示一週的第幾天
30 20 8-14,22-28 * * test $(date +%u) -eq 1 && /usr/local/bin/backup.sh >> /var/log/backup.log 2>&1
date +%u ：顯示一週的第幾天