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

Working Swift recordsdata as scripts

It’s attainable to run a Swift file straight from the command line when you add a hashbang) to the start of the file. This fashion you do not have to manually compile the code utilizing the swiftc command. You may merely give the file the executable permission flag and the system will name the Swift REPL beneath the hood, so our app may be evaluated routinely. 🔨

#!/usr/bin/env swift

print("Hiya, world!")

For instance this most important.swift file above may be marked as an executable file, and we will merely name it by way of the ./most important.swift command afterward (you simply have to make use of chmod just one time).

chmod +x most important.swift 
./most important.swift  
# Hiya, world!

The fantastic thing about this methodology is which you could quickly take a look at your Swift command line snippets. You may even place the completed Swift scripts beneath the /usr/native/bin/ listing with out the swift file extension to make them accessible “globally” in your working system consumer. 💪

Utilizing command line arguments in Swift

The CommandLine enum makes it very straightforward to fetch the arguments handed to our Swift utility or script. You may entry each argument utilizing the arguments variable as an array of Strings, however additionally it is attainable to get the uncooked knowledge 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)
}

You need to observe that the primary argument is all the time the trail of the present script, so if you’re solely searching for 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 hiya world
# Script: most important.swift
# Variety of arguments: 2
# Arguments:
# - hiya
# - world

In Xcode you possibly can add customized arguments beneath 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 atmosphere in Swift Identical to we will entry command line arguments, it’s attainable to look at the present course of together with some {hardware} info and atmosphere 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("Surroundings")

print(data.atmosphere)

The atmosphere variables property is a Dictionary the place each the keys and the values can be found as strings, so that you might need to parse them if you’re searching for totally different worth sorts. You may arrange atmosphere customized variables in Xcode similar to arguments, or you possibly can move them by way of the command line earlier than you execute the Swift script utilizing the export command.

Customary enter and output in Swift

You should use the print perform to write down textual content to the usual output, however you must observe that the print perform has a variadic objects definition, so you possibly can move round a number of arguments and a customized separator & terminator parameter to show extra superior outputs.

There’s additionally a normal error stream, which is a part of the normal streams in fact, however what’s fascinating about it’s which you could additionally write to this channel via the FileHandle.standardError property there’s fairly a sublime answer on a Stack Overflow thread initially created by Rob Napier, I’ll embrace that one right here as effectively. 🙏

One other nice characteristic of the print perform is the to parameter, which might settle for a customized TextOutputStream so you possibly can wrap the stderr stream in a customized object or you may as well create customized output handlers and separate your print statements e.g. by context when you want.

#!/usr/bin/env swift
import Basis


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


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


last class StandardErrorOutputStream: TextOutputStream {
    func write(_ string: String) {
        FileHandle.standardError.write(Knowledge(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.")
    strive console.run(group, enter: enter)
}
catch {
    console.error("(error)")
    exit(1)
}

You should use each answer via the Swift Bundle Supervisor, the setup course of is kind of straightforward, you may discover extra tutorials concerning the Swift Argument Parser and I believe that it’s more durable to seek out correct docs for ConsoleKit, so yeah… anyway, they’re nice libraries you will not remorse utilizing them. 😉

Make the most of the Swift Bundle Supervisor

The Swift Bundle Supervisor is without doubt one of the neatest thing concerning the Swift programming language. I actually like it and I take advantage of it virtually each 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 advanced rather a lot throughout the previous few months, when you check out the Swift Evolution dashboard you possibly can observe these modifications, the latest replace was the introduction of customized, user-defined Bundle Collections, however if you’re searching for packages you possibly can all the time check out the Swift Bundle Index web site. 👍