How can I shut down or reboot Ubuntu using terminal commands?

For Shutdown:
$sudo poweroff
(or)
$sudo shutdown -h now
(or)
$sudo halt
(or)
$sudo init 0
For Restart:
$sudo reboot
(or)
$sudo shutdown -r now
(or)
$sudo init 6

For Ubuntu 15.04 and later:
systemctl poweroff
systemctl reboot
systemctl suspend
systemctl hibernate
systemctl hybrid-sleep

Ubuntu 16.04 no need of say sudo also
To shutdown :
poweroff
To Reboot :
reboot