Determine OS X version from the command line

There are a few ways to determine what version of OSX you are on.

In the GUI, you can easily click the Apple menu () at the top left of your screen, and choose About This Mac. The version of OS X will be printed underneath the large bold Mac OS X title. Clicking on the Version XYZ text will reveal the Build number.

If you're writing a script though, you may wish to access this programmatically. There are several ways:

System Profiler

1.9.2 kevin-macbookpro:~ $ system_profiler SPSoftwareDataType
Software:

System Software Overview:

 System Version: Mac OS X 10.7.4 (11E53)
 Kernel Version: Darwin 11.4.0
 Boot Volume: San Francisco
 Boot Mode: Normal
 Computer Name: Kevin Elliott’s MacBook Pro
 User Name: Kevin Elliott (kevin)
 Secure Virtual Memory: Enabled
 64-bit Kernel and Extensions: Yes
 Time since boot: 1 day12:47

sw_vers

1.9.2 kevin-macbookpro:~ $ sw_vers
ProductName: Mac OS X
ProductVersion: 10.7.4
BuildVersion: 11E53

Mac OS X user defaults system

1.9.2 kevin-macbookpro:~ $ defaults read loginwindow SystemVersionStampAsString
10.7.4

There are further options but they are not as optimized and simple to use. These should be sufficient!