Since OS X 10.5 a command called PlistBuddy has been available.
It's useful for things like extracting the version number out of your Info.plist during a Run Script Build Phase.
PlistBuddy wasn't in my existing path, I found it at
/usr/libexec/PlistBuddy -c "Print :CFBundleVersion" Info.plist
Outputs: 0.14, or whatever the value of the CFBundleVersion key in Info.plist is.