Execute shell/bash commands from Swift

Bash.swift

import UIKit

protocol CommandExecuting {
    func run(commandName: String, arguments: [String]) throws -> String
}

enum BashError: Error {
    case commandNotFound(name: String)
}

struct Bash: CommandExecuting {
    func run(commandName: String, arguments: [String] = []) throws -> String {
        return try run(resolve(commandName), with: arguments)
    }

    private func resolve(_ command: String) throws -> String {
        guard var bashCommand = try? run("/bin/bash" , with: ["-l", "-c", "which \(command)"]) else {
            throw BashError.commandNotFound(name: command)
        }
        bashCommand = bashCommand.trimmingCharacters(in: NSCharacterSet.whitespacesAndNewlines)
        return bashCommand
    }

    private func run(_ command: String, with arguments: [String] = []) throws -> String {
        let process = Process()
        process.launchPath = command
        process.arguments = arguments
        let outputPipe = Pipe()
        process.standardOutput = outputPipe
        process.launch()
        let outputData = outputPipe.fileHandleForReading.readDataToEndOfFile()
        let output = String(decoding: outputData, as: UTF8.self)
        return output
    }
}

let bash: CommandExecuting = Bash()
if let lsOutput = try? bash.run(commandName: "ls", arguments: []) { print(lsOutput) }
if let lsWithArgumentsOutput = try? bash.run(commandName: "ls", arguments: ["-la"]) { print(lsWithArgumentsOutput) }

IMHO, Swift's dynamicMember syntactic sugar blurs the line between compile-time failures and runtime failures. If you introduce the bash.ls() syntax vs. bash.run(commandName: "ls") syntax, you are kind of suggesting that the ls command is a built-in API command that is not subject to the runtime command not found error. I wouldn't use dynamicMember in an interface without a good reason (but that's just me :) ).

With my implementation, ls() will not autocomplete if working inside Xcode, and passing it as a string argument is just doing the same thing but with more steps. Unless you define a symbol, there’s no way to avoid runtime errors.

I wouldn’t use dynamicMember in production code either, but for scripting it minimizes all the boilerplate we’re used to autocompleting away

Also, perhaps it would be beneficial to factor out which apart from run to allow a consumer to decide what exactly to execute:: https://gist.github.com/gary17/b6c8b662da36cefee7010cd4bdcb2ee6

This works great, thank you for the gist!

I do get an error when using the command, although the given command is still executed. I get /bin/bash: /etc/profile: Operation not permitted before every print out of my original command.

Example code:

let cli = Bash()
if let output = try? cli.run(commandName: "pwd") {
    print(output)
}

I did change the import from UiKit to AppKit since I'm developing for MacOS.