Using the Build System

Swift’s build system provides a convention-based system for building libraries and executables, and sharing code across different projects.

These examples assume you have made swift available in your path; see Installing for more information. Once available, you can invoke the build system using swift build:

$ swift build --help
OVERVIEW: Build sources into binary products
...

Creating a Package

To create a new Swift package, first create and navigate to a new directory named Hello:

$ mkdir Hello
$ cd Hello

Every package must have a manifest file called Package.swift in its root directory. If the manifest file is blank, the package manager will build the package using conventional defaults. Create an empty manifest using:

$ touch Package.swift

When using the defaults, the package manager expects all source code to be contained in aSources/ subdirectory. Create that with:

$ mkdir Sources

Building an Executable

By default, a directory that contains a file called main.swift will compile that file into a binary executable with the name of the package.

In this example, the package will produce an executable named Hello that outputs “Hello, world!”.

Create a file called main.swift in the Sources/ directory and using your editor of choice, enter the following code:

print("Hello, world!")

Compile the package by running the swift build command:

$ swift build

After the command finishes, the built products will be available in the .build directory. Run the Hello program with the following command:

$ .build/debug/Hello
Hello, world!

As a next step, let’s define a new sayHello(name:) function in a new source file, and have the executable call that instead of calling print(_:) directly.

Working with Multiple Source Files

Create a new file in the Sources/ directory called Greeter.swift, and enter the following code:

func sayHello(name: String) {
    print("Hello, \(name)!")
}

The sayHello(name:) function takes a single String argument and prints our “Hello” greeting before, substituting the word “World” with the function argument.

Now, open main.swift again, and replace the existing contents with the following code:

if Process.arguments.count != 2 {
    print("Usage: hello NAME")
} else {
    let name = Process.arguments[1]
    sayHello(name: name)
}

Rather than using a hardcoded name as before, main.swift now reads from the command line arguments. And instead of invoking print(_:) directly, main.swift now calls thesayHello(name:) method. Because the method is part of the Hello module, no importstatement is necessary.

Run swift build and try out the new version of Hello:

$ swift build
$ .build/debug/Hello `whoami`

To learn about the Swift Package Manager, including how to build modules, import dependencies, and map system libraries, see the Swift Package Manager section of the website.

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