This post is mostly a brain dump of what it takes to use Swift for command line scripting.

Update: I've added -S to env. This makes things compatible with recent versions of FreeBSD. There doesn't appear to be a portable solution for Linux because it treats the entire line after the first space as a single argument rather than splitting into multiple arguments and its version of env doesn't support -S.

#!/usr/bin/env -S xcrun --toolchain <X> swift

import Foundation

The first step is to decide which version of Swift you want to use. Replace <X> with the toolchain identifier from Xcode.app/Contents/Developer/Toolchains/<X>/ToolchainInfo.plist.

• com.apple.dt.toolchain.Swift_2_3 - this is the toolchain you get if you don't specify a toolchain or use /usr/bin/swift directly (when executing Swift scripts on macOS Sierra or earlier)
• com.apple.dt.toolchain.XcodeDefault - this is the toolchain you get if you specify an invalid toolchain identifier.

If in doubt, consult this handy table:

I wish you could specify the specific Swift version you wanted instead (rdar://problem/28409078)

Options

You can also pass options to Swift this way:

#!/usr/bin/env -S xcrun --toolchain <X> swift -F/my/frameworks -framework MyUtils.framework -D FLAG

This works just like invoking the compiler or REPL. -F adds a framework search path. -framework adds a framework to load. -D adds a conditional compilation flag.

If you have a collection of personal utilities you'd like to use from scripts just build a framework, drop it somewhere like /usr/local/lib, and specify the path and framework name in your script.

If you'd prefer something more automated, check out cato which handles picking a Swift version, uses Cocoapods to download frameworks, builds them, and invokes your script with Swift.

Args and Misc

In Swift 3 use CommandLine.arguments. Index zero is the command itself (in this case your script).

Remember you still need to import <framework>, including Foundation.

Use Process to launch other commands. You can hook its standard input/output up to a Pipe if you want to capture the output.

Conclusion

Are you writing scripts in Swift? Have any tips or tricks? Please leave a comment!