Template for setting up swift scripts

swift-script-template.swift

#!/usr/bin/env swift

#if os(OSX)
    import Darwin
#else
    import Glibc
#endif

import Foundation

// MARK: Failure

@noreturn func fail(_ msg: String) {
    print("Error: \(msg)")
    exit(1)
}

func run(_ command: String, allowFailure: Bool = false) {
    let result = system(command)
    if allowFailure { return }
    else if result != 0 {
      fail("error code \(result)")
    }
}

func passes(_ command: String) -> Bool {
  return system(command) == 0
}

func getInput() -> String {
  return readLine(strippingNewline: true) ?? ""
}

func commandExists(_ command: String) -> Bool {
  return system("hash \(command) 2>/dev/null") == 0
}

// MARK: Command

protocol Command {
  static var description: String { get }
  static func execute(with args: [String], in directory: String)
}

extension Command {
  static var description: String {
    return ""
  }
}

// MARK: Tree

var commandTree: [String : Command.Type] = [:]

// MARK: Help

struct Help: Command {
    static func execute(with args: [String], in directory: String) {
      var help = "Available Commands:\n\n"
      help += commandTree
          .map { key, val in "\t\(key): \(val.description)"}
          .joined(separator: "\n")
      help += "\n"
      print(help)
    }
}

commandTree["help"] = Help.self

// MARK: Custom Commands

// ... define custom Command types and add to commandTree here

// MARK: Execution

var iterator = Process.arguments.makeIterator()

guard let directory = iterator.next() else {
  fail("no directory")
}
guard let commandKey = iterator.next() else {
  fail("no command")
}
guard let command = commandTree[commandKey] else {
  fail("command \(commandKey) doesn't exist")
}

let arguments = Array(iterator)

command.execute(with: arguments, in: directory)