Swift 3.0+更新

func SYSTEM_VERSION_EQUAL_TO(version: String) -> Bool {
    return UIDevice.current.systemVersion.compare(version, options: .numeric) == ComparisonResult.orderedSame
}

func SYSTEM_VERSION_GREATER_THAN(version: String) -> Bool {
    return UIDevice.current.systemVersion.compare(version, options: .numeric) == ComparisonResult.orderedDescending
}

func SYSTEM_VERSION_GREATER_THAN_OR_EQUAL_TO(version: String) -> Bool {
    return UIDevice.current.systemVersion.compare(version, options: .numeric) != ComparisonResult.orderedAscending
}

func SYSTEM_VERSION_LESS_THAN(version: String) -> Bool {
    return UIDevice.current.systemVersion.compare(version, options: .numeric) == ComparisonResult.orderedAscending
}

func SYSTEM_VERSION_LESS_THAN_OR_EQUAL_TO(version: String) -> Bool {
    return UIDevice.current.systemVersion.compare(version, options: .numeric) != ComparisonResult.orderedDescending
}

马特·汤普森分享了一种非常简便的方法

switch UIDevice.currentDevice().systemVersion.compare("8.0.0", options: NSStringCompareOptions.NumericSearch) {
case .OrderedSame, .OrderedDescending:
    println("iOS >= 8.0")
case .OrderedAscending:
    println("iOS < 8.0")
}

对于iOS，请尝试:

var systemVersion = UIDevice.current.systemVersion

对于OS X，尝试:

var systemVersion = NSProcessInfo.processInfo().operatingSystemVersion

如果你只是想检查用户是否至少运行了一个特定的版本，你也可以使用以下Swift 2功能，它适用于iOS和OS X:

if #available(iOS 9.0, *) {
    // use the feature only available in iOS 9
    // for ex. UIStackView
} else {
    // or use some work around
}

但不建议检查操作系统版本。最好检查您想要使用的功能在设备上是否可用，而不是比较版本号。 对于iOS，如前所述，你应该检查它是否响应选择器; 如:

if (self.respondsToSelector(Selector("showViewController"))) {
    self.showViewController(vc, sender: self)
} else {
    // some work around
}

斯威夫特5

func run() {
    let version = OperatingSystemVersion(majorVersion: 13, minorVersion: 0, patchVersion: 0)
    if ProcessInfo.processInfo.isOperatingSystemAtLeast(version) {
        runNewCode()
    } else {
        runLegacyCode()
    }
}

func runNewCode() {
    guard #available(iOS 13.0, *) else {
        fatalError()
    }
    // do new stuff
}

func runLegacyCode() {
    // do old stuff
}

如果你正在使用Swift 2，并且你想要检查操作系统版本以使用某个API，你可以使用新的可用性特性:

if #available(iOS 8, *) {
    //iOS 8+ code here.
}
else {
    //Code for iOS 7 and older versions.
    //An important note: if you use #availability, Xcode will also 
    //check that you don't use anything that was introduced in iOS 8+
    //inside this `else` block. So, if you try to use UIAlertController
    //here, for instance, it won't compile. And it's great.
}

我写这个答案是因为它是谷歌中swift 2 check系统版本查询的第一个问题。

注:iOS 8.0及以上版本支持。OS X v10.10及以上版本

var majorVersion: Int    { return NSProcessInfo.processInfo().operatingSystemVersion.majorVersion }
var minorVersion: Int    { return NSProcessInfo.processInfo().operatingSystemVersion.minorVersion }
var patchVersion: Int    { return NSProcessInfo.processInfo().operatingSystemVersion.patchVersion }
var myOSVersion:  String { return NSProcessInfo.processInfo().operatingSystemVersionString        }