Nproc

The nproc command prints the number of processors (cores).

Provided by
Not all distributions provide this command, but most (all?) of the ones that do incorporate this from the GNU Coreutils: and use its man page

Related Commands
All of these relate to system-wide information.
 * date - set or show the time.
 * arch - show CPU hardware details.
 * uname - Show host and kernel information.
 * hostname - Set or show the host's name.
 * hostid - Show the host's numeric ID.
 * uptime - Show system uptime and recent load averages.