How can I get numbers of CPU of Sun Solaris by command?

With modern CPUs and their multi-core, multi-thread technologies, you need to define more precisely what you want to count but in your case, psrinfo better suits the job:

psrinfo -p

Note that prtdiag wasn't designed to be parseable and might return a very different output depending on the hardware.

Here is a simple set of pipes using psrinfo:

psrinfo -v | grep ^Status | tail -1 | awk '{x = $5 + 1; print "CPUs: " x;}'

Example output:

CPUs: 6