system_profiler

Report system hardware and software configuration.

Display a full system profiler report which can be opened by System Profiler.app:

system_profiler -xml > MyReport.spx

Display a hardware overview (Model, CPU, Memory, Serial, etc):

system_profiler SPHardwareDataType

Print the system serial number:

system_profiler SPHardwareDataType|grep "Serial Number (system)" |awk '{print $4}'