Simple command to draw a rect.

drawRect.swift

/*
 Tested on OS X 10.11 and Ubuntu 15.10

 Exmaple: `$ drawRect 4 3` should output this:
 ┌──┐
 │  │
 └──┘
 */

// MARK: - Data Structures

struct Size {
  static let zero = Size(width: 0, height: 0)

  let width: Int
  let height: Int
}

struct Rect {
  static let space   = " "
  static let newline = "\n"
  static let corners = Corners()
  static let lines   = Lines()

  struct Corners {
    let topLeft     = "┌"
    let topRight    = "┐"
    let bottomLeft  = "└"
    let bottomRight = "┘"
  }

  struct Lines {
    let vertical   = "│"
    let horizontal = "─"
  }
}

// MARK: - Argument Parsing

func processInput() -> Size? {
 let argc = Process.argc
  let args = Process.arguments

  guard argc == 3,
        let width = Int(args[1]),
        let height = Int(args[2]) else {
    return nil
  }

  return Size(width: width, height: height)
}

// MARK: - Output

func printUsage() {
  print("Usage: drawRect width height")
}

func drawRect(size size: Size) {
  guard size.width > 1 && size.height > 1 else {
    print(Rect.corners.topLeft + Rect.corners.topRight + Rect.newline + 
          Rect.corners.bottomLeft + Rect.corners.bottomRight)
    return
  }

  var image = ""

  for y in 0..<size.height {
    for x in 0..<size.width {
      if x == 0 {
        if y == 0 {
          image += Rect.corners.topLeft
        } else if y == size.height - 1 {
          image += Rect.corners.bottomLeft
        } else {
          image += Rect.lines.vertical
        }
      } else if x == size.width - 1 {
        if y == 0 {
          image += Rect.corners.topRight
        } else if y == size.height - 1 {
          image += Rect.corners.bottomRight
        } else {
          image += Rect.lines.vertical
        }
        image += Rect.newline
      } else {
        if y == 0 || y == size.height - 1 {
          image += Rect.lines.horizontal
        } else {
          image += Rect.space
        }
      }
    }
  }

  print(image)
}

// MARK: - Flow

if let size = processInput() {
  drawRect(size: size)
} else {
  printUsage()
}