Swift command line tools
In this book, we have already worked with a terminal tool—a Swift REPL console. We start it by entering the xcrun swift command in the terminal. It starts the REPL, and we can enter Swift code and evaluate it.
xcrun
To start a REPL, we actually used two tools: xcrun and swift. xcrun is an Xcode command-line tool runner. It helps you run a command-line tool by its name from the active developer directory. When you have installed many versions of Xcode, you can select which one to use while executing a command-line tool. You can do this in Xcode by going to Xcode | Preference | Locations | Command Line Tools, or by running the xcode-select command from the terminal. In this way, xcrun allows you to avoid specifying the full path in the command-line tool you want to run, and makes the process of running it much simpler.
xcrun has a few more interesting options, and you should experiment with them. To get help, run the xcrun -h help command, which is usually available...
