Utilities for writing command line code in Swift

Bash.swift

#!/usr/bin/env swift

import Foundation

struct TerminationStatus: Error {
  let code: Int32
}

func run(_ command: Command) throws {
  print(command.rendered.joined(separator: " "))
  let task = Process()
  task.launchPath = "/usr/bin/env"
  task.arguments = command.rendered
  task.launch()
  task.waitUntilExit()

  if task.terminationStatus != 0 {
    throw TerminationStatus(code: task.terminationStatus)
  }
}

@dynamicMemberLookup
@dynamicCallable
struct Command {
  typealias Component = (String, [String: String?])
  let components: [Component]

  init(components: [Component] = []) {
    self.components = components
  }

  var rendered: [String] {
    components.flatMap { c in
      [c.0] + c.1.flatMap { ["-\($0.0)", $0.1] }.compactMap { $0 }
    }
  }

  subscript(dynamicMember member: String) -> Self {
    addingComponent(member)
  }

  func dynamicallyCall(withKeywordArguments args: KeyValuePairs<String, String?>) throws {
    try run(self.addingArguments(args))
  }

  func addingComponent(_ component: String) -> Command {
    Command(
      components: components + [(component, [:])]
    )
  }

  func addingArguments(_ arguments: [String, String?]) -> Command {
    guard components.count > 0 else {
      return Command(components: [("", arguments)])
    }
    var c = self
    c.components.last?.1 += arguments
    return c
  }
}

// Examples

let cmd = Command()

try cmd.xcodebuild.archive(
  project: "projectPath/ProjectName.xcodeproj",
  scheme: "production"
)