Incidentally, on a Mac, this will give you your number of cores, along with other handy stuff:

system_profiler SPHardwareDataType

Hardware:

    Hardware Overview:

      Model Name: MacBook Pro
      Model Identifier: MacBookPro5,1
      Processor Name: Intel Core 2 Duo
      Processor Speed: 2.4 GHz
      Number of Processors: 1
      Total Number of Cores: 2
      L2 Cache: 3 MB
      Memory: 4 GB
      Bus Speed: 1.07 GHz
      Boot ROM Version: MBP51.007E.B05
      SMC Version (system): 1.41f2
      Serial Number (system): [snip]
      Hardware UUID: [snip]
      Sudden Motion Sensor:
          State: Enabled