iOS Development

Tips on how to construct higher command line apps and instruments utilizing Swift?

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The following tips will enable you to to create superb CLI instruments, utility apps, server aspect tasks or terminal scripts utilizing the Swift language.

Swift

Operating Swift information as scripts

It’s potential to run a Swift file straight from the command line should 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’ll be able to merely give the file the executable permission flag and the system will name the Swift REPL beneath the hood, so our app could be evaluated routinely. 🔨


#!/usr/bin/env swift

print("Hiya, world!")


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


chmod +x essential.swift 
./essential.swift  


The fantastic thing about this technique is you could quickly take a look at your Swift command line snippets. You’ll be able to even place the completed Swift scripts beneath the /usr/native/bin/ listing with out the swift file extension to make them out there “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 software or script. You’ll be able to entry each argument utilizing the arguments variable as an array of Strings, however additionally it is potential 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 word that the primary argument is all the time the trail of the present script, so in case you are solely searching for the enter arguments you should use the dropFirst() technique to return a subset of the enter strings. Often every argument is separated by an area character.


./essential.swift hey world




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



Course of information and setting in Swift

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


#!/usr/bin/env swift
import Basis

let information = ProcessInfo.processInfo

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

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

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


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

print("Atmosphere")

print(information.setting)


The setting 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 in case you are searching for completely different worth sorts. You’ll be able to arrange setting customized variables in Xcode identical to arguments, or you’ll be able to go them through the command line earlier than you execute the Swift script utilizing the export command.





Normal enter and output in Swift

You should utilize the print perform to write down textual content to the usual output, however it’s best to word that the print perform has a variadic gadgets definition, so you’ll be able to go round a number of arguments and a customized separator & terminator parameter to show extra superior outputs.


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


One other nice function of the print perform is the to parameter, which may settle for a customized TextOutputStream so you’ll be able to wrap the stderr stream in a customized object or you too can 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"
    .knowledge(utilizing: .utf8)
    .map(FileHandle.standardError.write)


closing 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 utilize each resolution via the Swift Package deal Supervisor, the setup course of is sort of straightforward, you will discover extra tutorials in regards to 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. 😉




Benefit from the Swift Package deal Supervisor

The Swift Package deal Supervisor is without doubt one of the neatest thing in regards to the Swift programming language. I actually like it and I take advantage of it nearly day-after-day. The truth that the package deal manifest file is outlined utilizing Swift itself makes it straightforward to make use of & perceive.



import PackageDescription

let package deal = Package deal(
    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 package deal supervisor developed quite a bit in the course of 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 Package deal Collections, however in case you are searching for packages you’ll be able to all the time check out the Swift Package deal Index web site. 👍




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