In this book, you have built and run many command-line tools in Xcode. Running in Xcode works great for testing programs and for learning programming. However, if you create a command-line tool to use in real life, then you will want to run it from the command line.
In a Mac, you typically use Terminal to run programs from the command line. The Terminal app is just a pretty interface to what is called a shell. There are a few different shells with catchy names like csh, sh, zsh, and ksh, but nearly all Mac users use bash.
To run a program from the command line, you enter the path of the program’s executable file in Terminal and press Return.
In Xcode, return to your gradeInTheShade project ...