How do I shutdown, restart, or log off Windows via a bat file?

The most common ways to use the shutdown command are:

• shutdown -s — Shuts down.
• shutdown -r — Restarts.
• shutdown -l — Logs off.

• shutdown -h — Hibernates.

  Note: There is a common pitfall wherein users think -h means "help" (which it does for every other command-line program... except shutdown.exe, where it means "hibernate"). They then run shutdown -h and accidentally turn off their computers. Watch out for that.

• shutdown -i — "Interactive mode". Instead of performing an action, it displays a GUI dialog.

• shutdown -a — Aborts a previous shutdown command.

The commands above can be combined with these additional options:

• -f — Forces programs to exit. Prevents the shutdown process from getting stuck.
• -t <seconds> — Sets the time until shutdown. Use -t 0 to shutdown immediately.
• -c <message> — Adds a shutdown message. The message will end up in the Event Log.

• -y — Forces a "yes" answer to all shutdown queries.

  Note: This option is not documented in any official documentation. It was discovered by these StackOverflow users.

I want to make sure some other really good answers are also mentioned along with this one. Here they are in no particular order.

• The -f option from JosephStyons
• Using rundll32 from VonC
• The Run box from Dean
• Remote shutdown from Kip

If you are on a remote machine, you may also want to add the -f option to force the reboot. Otherwise your session may close and a stubborn app can hang the system.

I use this whenever I want to force an immediate reboot:

shutdown -t 0 -r -f

For a more friendly "give them some time" option, you can use this:

shutdown -t 30 -r

As you can see in the comments, the -f is implied by the timeout.

Brutus 2006 is a utility that provides a GUI for these options.