命令tr
$ df -h
Filesystem Size Used Avail Use% Mounted on
udev 126G 0 126G 0% /dev
tmpfs 26G 4.0M 26G 1% /run
/dev/sda2 548G 50G 471G 10% /
tmpfs 126G 0 126G 0% /sys/fs/cgroup
/dev/sda1 511M 7.9M 504M 2% /boot/efi
/dev/sdb1 2.0T 4.7G 1.9T 1% /data
$ df -h | tr a-z A-Z