Are there any Swift-based command-line tools for web scraping?

Swift is not as commonly used for web scraping as languages like Python, JavaScript (Node.js), or Ruby, largely because the ecosystem for such tasks is not as mature or extensive. However, that does not mean it is impossible to perform web scraping using Swift, especially since Swift can be used to write command-line tools that run on macOS and Linux.

To scrape websites using Swift, you would typically use URLSession to make HTTP requests and a library like SwiftSoup or Kanna to parse HTML.

SwiftSoup is a Swift library that provides JQuery-like syntax for parsing and manipulating HTML. Kanna is another XML/HTML parser for Swift.

Here's a simple example of how you might use SwiftSoup in a Swift command-line tool to scrape a website:

First, you'll need to add SwiftSoup to your Swift package by editing the Package.swift file:

// swift-tools-version:5.3
import PackageDescription

let package = Package(
    name: "MyWebScraper",
    dependencies: [
        .package(url: "https://github.com/scinfu/SwiftSoup.git", from: "2.3.2")
    ],
    targets: [
        .target(
            name: "MyWebScraper",
            dependencies: ["SwiftSoup"]
        )
    ]
)

Then, you could write a simple Swift script to scrape data:

import Foundation
import SwiftSoup

let urlString = "http://example.com"

// Create a URL instance
if let url = URL(string: urlString) {
    // Start a URL session
    let task = URLSession.shared.dataTask(with: url) { data, response, error in
        // Ensure there's no error and there is data
        if let error = error {
            print("Error fetching the URL: \(error)")
            return
        }

        guard let data = data else {
            print("No data received.")
            return
        }

        // Parse the data with SwiftSoup
        do {
            let html = String(data: data, encoding: .utf8)!
            let document = try SwiftSoup.parse(html)
            let elements = try document.select("a") // Example: Select all links

            for element in elements.array() {
                let text = try element.text()
                let href = try element.attr("href")
                print("\(text) -> \(href)")
            }
        } catch {
            print("Error parsing HTML: \(error)")
        }
    }

    task.resume()
}

// Keep the program running until the async task is completed
RunLoop.main.run()

This script performs an HTTP GET request to "http://example.com", then parses the HTML and prints out the text and href attributes for all anchor tags.

Keep in mind that Swift command-line tools for web scraping, such as the one in the example above, will work well but might not have the same level of support or community as tools in other languages. Additionally, handling JavaScript-heavy websites might be more challenging in Swift when compared to using tools like Puppeteer or Playwright in Node.js, which can control a headless browser for more complex scraping tasks.

For complex scraping tasks involving JavaScript execution or browser emulation, you might want to consider using other tools and perhaps calling them from your Swift code, if necessary.