Command-line Swift

Swift is not limited to Xcode apps. You can write small command-line programs for scripts, experiments, and tools.

A simple program

A Swift file can contain top-level code:

let name = "Swift"
print("Hello, \(name)")

Save it as main.swift, then run it:

swift main.swift

For larger tools, create a Swift package:

swift package init --type executable
swift run

Swift Package Manager creates files for a buildable command-line project.

Reading arguments

Command-line arguments are available through CommandLine.arguments:

let arguments = CommandLine.arguments

if arguments.count > 1 {
    print("Hello, \(arguments[1])")
} else {
    print("Usage: greet <name>")
}

The first argument is the executable path. User-provided arguments start after that.

Basic input and output

Use print for output:

print("Enter your name:")

Use readLine() for simple input:

if let name = readLine(), !name.isEmpty {
    print("Hello, \(name)")
}

readLine() returns an optional because input may be unavailable.

Why CLI practice helps app work

Command-line Swift removes UI concerns. You can practice types, optionals, functions, decoding, errors, and tests in a smaller environment before adding SwiftUI.

This is also useful for app tooling: data importers, local build helpers, migration scripts, and small developer utilities.

What to carry forward

• Swift can run as scripts or executable packages
• swift main.swift runs a simple file
• Swift Package Manager can create command-line tools
• CommandLine.arguments reads CLI arguments
• readLine() returns an optional
• CLI programs are useful for practicing core Swift without UI

Next, you will learn generics for reusable typed code.