The best way to construct higher command line apps and instruments utilizing Swift?

Working Swift information as scripts

It’s doable to run a Swift file straight from the command line should you add a hashbang to the start of the file. This manner you do not have to manually compile the code utilizing the swiftc command. You’ll be able to merely give the file the executable permission flag and the system will name the Swift REPL underneath the hood, so our app could be evaluated routinely. 🔨

#!/usr/bin/env swift

print("Hiya, world!")

For instance this most important.swift file above could be marked as an executable file, and we are able to merely name it through the ./most important.swift command in a while (you simply have to make use of chmod just one time).

chmod +x most important.swift 
./most important.swift  

The fantastic thing about this methodology is which you could quickly check your Swift command line snippets. You’ll be able to even place the completed Swift scripts underneath the /usr/native/bin/ listing with out the swift file extension to make them out there “globally” in your working system person. 💪

Utilizing command line arguments in Swift

The CommandLine enum makes it very straightforward to fetch the arguments handed to our Swift software or script. You’ll be able to entry each argument utilizing the arguments variable as an array of Strings, however additionally it is doable to get the uncooked information utilizing the argc and unsafeArgv properties.

#!/usr/bin/env swift


let script = CommandLine.arguments[0]
print("Script:", script)


let inputArgs = CommandLine.arguments.dropFirst()
print("Variety of arguments:", inputArgs.rely)

print("Arguments:")
for arg in inputArgs {
    print("-", arg)
}

It’s best to word that the primary argument is at all times the trail of the present script, so in case you are solely in search of the enter arguments you should utilize the dropFirst() methodology to return a subset of the enter strings. Often every argument is separated by an area character.

./most important.swift good day world

In Xcode you’ll be able to add customized arguments underneath the Edit Scheme… menu merchandise while you click on on the present scheme, search for the Arguments tab and use the Arguments Handed On Launch part.

Course of data and setting in Swift

Identical to we are able to entry command line arguments, it’s doable to look at the present course of together with some {hardware} info and setting variables.

#!/usr/bin/env swift
import Basis

let data = ProcessInfo.processInfo

print("Course of data")
print("Course of identifier:", data.processIdentifier)
print("System uptime:", data.systemUptime)
print("Globally distinctive course of id string:", data.globallyUniqueString)
print("Course of identify:", data.processName)

print("Software program data")
print("Host identify:", data.hostName)
print("OS main model:", data.operatingSystemVersion.majorVersion)
print("OS model string", data.operatingSystemVersionString)

print("{Hardware} data")
print("Lively processor rely:", data.activeProcessorCount)
print("Bodily reminiscence (bytes)", data.physicalMemory)


print("Arguments")
print(ProcessInfo.processInfo.arguments)

print("Setting")

print(data.setting)

The setting variables property is a Dictionary the place each the keys and the values can be found as strings, so that you may need to parse them in case you are in search of totally different worth sorts. You’ll be able to arrange setting customized variables in Xcode identical to arguments, or you’ll be able to move them through the command line earlier than you execute the Swift script utilizing the export command.

Customary enter and output in Swift

You need to use the print perform to jot down textual content to the usual output, however it is best to word that the print perform has a variadic objects definition, so you’ll be able to move round a number of arguments and a customized separator & terminator parameter to show extra superior outputs.

There may be additionally an ordinary error stream, which is a part of the normal streams after all, however what’s fascinating about it’s which you could additionally write to this channel by means of the FileHandle.standardError property there’s fairly a chic answer on a Stack Overflow thread initially created by Rob Napier, I will embody that one right here as properly. 🙏

One other nice characteristic of the print perform is the to parameter, which might settle for a customized TextOutputStream so you’ll be able to wrap the stderr stream in a customized object or it’s also possible to create customized output handlers and separate your print statements e.g. by context should you want.

#!/usr/bin/env swift
import Basis


print("This", "is", "enjoyable", separator: "-", terminator: "!")


"This goes to the usual error output"
    .information(utilizing: .utf8)
    .map(FileHandle.standardError.write)


closing class StandardErrorOutputStream: TextOutputStream {
    func write(_ string: String) {
        FileHandle.standardError.write(Information(string.utf8))
    }
}

var outputStream = StandardErrorOutputStream()
print("That is additionally an error", to: &outputStream)



func clear() {
    print("u{1B}[2J")
    print("u{1B}[(1);(0)H", terminator: "")
}

print("foooooooooooooooooooooo")
clear()
print("Hello, world!")



print("u{1b}[31;1mu{1b}[40;1m("Hello, world!")u{1b}[m")
print("u{1b}[32;1m("Hello, world!")u{1b}[m")


print("Please enter your input:")
guard let input = readLine(strippingNewline: true) else {
    fatalError("Missing input")
}
print(input)

The second half of the snippet is full of ANSI escape codes which I like quite a lot, because it can make our terminal output quite beautiful. The only problem is that they don’t work in Xcode at all (come-on Apple, please support this…). You can clear the console or change the background / foreground color of the output by using these codes.

There are quite a lot of libraries on GitHub that you can use to print colorful output, for example ColorizeSwift, ANSITerminal, ANSIEscapeCode and many more cool ones.

The very last thing that I’d like to show you is the readLine function, which you can use to read a line from the standard input. This comes handy if you need to get user input from the command line.

Use an argument parser library

If you are looking for a type-safe argument parser written in Swift, you should definitely take a look at the Swift Argument Parser library. It is created and maintained by Apple, so it’s kind of an official solution for this particular issue, but IMHO it lacks some advanced features.

This is the main reason why I prefer the Vapor command API built on top of the ConsoleKit library. Both libraries can parse arguments, options and flags, but ConsoleKit is also capable of displaying progress indicators, it features multiple command groups, secure input, auto-completion, multiple log levels and many more.

import Foundation
import ConsoleKit

final class HelloCommand: Command {
        
    struct Signature: CommandSignature {

        @Argument(name: "name", help: "The name to say hello")
        var name: String

        @Option(name: "greeting", short: "g", help: "Greeting used")
        var greeting: String?

        @Flag(name: "capitalize", short: "c", help: "Capitalizes the name")
        var capitalize: Bool
    }

    static var name = "hello"
    let help = "This command will say hello to a given name."

    func run(using context: CommandContext, signature: Signature) throws {
        let greeting = signature.greeting ?? "Hello"
        var name = signature.name
        if signature.capitalize {
            name = name.capitalized
        }
        print("(greeting) (name)!")
        
        
        let bar = context.console.progressBar(title: "Hello")
        bar.start()
        
        bar.succeed()
        
        
        let foo = context.console.ask("What?")
        print(foo)
        
        
        let baz = context.console.ask("Secure what?", isSecure: true)
        print(baz)
        
        
        let c = context.console.choose("Make a choice", from: ["foo", "bar", "baz"])
        print(c)

        
    }
}


import Basis
import ConsoleKit

let console: Console = Terminal()
var enter = CommandInput(arguments: CommandLine.arguments)
var context = CommandContext(console: console, enter: enter)

var instructions = Instructions(enableAutocomplete: true)
instructions.use(HelloCommand(), as: HelloCommand.identify, isDefault: false)

do {
    let group = instructions.group(assist: "Utilizing ConsoleKit with out Vapor.")
    attempt console.run(group, enter: enter)
}
catch {
    console.error("(error)")
    exit(1)
}

You need to use each answer by means of the Swift Bundle Supervisor, the setup course of is kind of straightforward, you will discover extra tutorials in regards to the Swift Argument Parser and I feel that it’s more durable to search out correct docs for ConsoleKit, so yeah… anyway, they’re nice libraries you will not remorse utilizing them. 😉

Benefit from the Swift Bundle Supervisor

The Swift Bundle Supervisor is likely one of the neatest thing in regards to the Swift programming language. I actually find it irresistible and I exploit it nearly every single day. The truth that the bundle manifest file is outlined utilizing Swift itself makes it straightforward to make use of & perceive.

import PackageDescription

let bundle = Bundle(
    identify: "myProject",
    platforms: [
        .macOS(.v10_15)
    ],
    dependencies: [
        .package(url: "https://github.com/vapor/console-kit", from: "4.1.0"),
    ],
    targets: [
        .executableTarget(name: "myProject",dependencies: [
            .product(name: "ConsoleKit", package: "console-kit"),
        ]),
        .testTarget(identify: "myProjectTests", dependencies: ["myProject"]),
    ]
)

The bundle supervisor developed rather a lot through the previous few months, should you check out the Swift Evolution dashboard you’ll be able to observe these adjustments, the newest replace was the introduction of customized, user-defined Bundle Collections, however in case you are in search of packages you’ll be able to at all times check out the Swift Bundle Index web site. 👍