How do I run a terminal command in a Swift script? (e.g. xcodebuild)

If you would like to use command line arguments "exactly" as you would in command line (without separating all the arguments), try the following.

(This answer improves off of LegoLess's answer and can be used in Swift 5)

import Foundation

func shell(_ command: String) -> String {
    let task = Process()
    let pipe = Pipe()
    
    task.standardOutput = pipe
    task.standardError = pipe
    task.arguments = ["-c", command]
    task.launchPath = "/bin/zsh"
    task.standardInput = nil
    task.launch()
    
    let data = pipe.fileHandleForReading.readDataToEndOfFile()
    let output = String(data: data, encoding: .utf8)!
    
    return output
}

// Example usage:
shell("ls -la")

Updated / safer function calls 10/23/21: It's possible to run into a runtime error with the above shell command and if so, try swapping to the updated calls below. You'll need to use a do catch statement around the new shell command but hopefully this saves you some time searching for a way to catch unexpected error(s) too.

Explanation: Since task.launch() isn't a throwing function it cannot be caught and I was finding it to occasionally simply crash the app when called. After much internet searching, I found the Process class has deprecated task.launch() in favor of a newer function task.run() which does throw errors properly w/out crashing the app. To find out more about the updated methods, please see: https://eclecticlight.co/2019/02/02/scripting-in-swift-process-deprecations/

import Foundation

@discardableResult // Add to suppress warnings when you don't want/need a result
func safeShell(_ command: String) throws -> String {
    let task = Process()
    let pipe = Pipe()
    
    task.standardOutput = pipe
    task.standardError = pipe
    task.arguments = ["-c", command]
    task.executableURL = URL(fileURLWithPath: "/bin/zsh") //<--updated
    task.standardInput = nil

    try task.run() //<--updated
    
    let data = pipe.fileHandleForReading.readDataToEndOfFile()
    let output = String(data: data, encoding: .utf8)!
    
    return output
}

Examples:

// Example usage capturing error:
do {
    try safeShell("ls -la")
}
catch {
    print("\(error)") //handle or silence the error here
}

// Example usage where you don't care about the error and want a nil back instead
let result = try? safeShell("ls -la")

// Example usage where you don't care about the error or the return value
try? safeShell("ls -la")

Note: For the last case where you are using try? and aren't using the result, for some reason the compiler still warns you even though it's marked as @discardableResult. This only happens with try?, not try within a do-try-catch block or from within a throwing function. Either way, you can safely ignore it.

The problem here is that you cannot mix and match Bash and Swift. You already know how to run Swift script from command line, now you need to add the methods to execute Shell commands in Swift. In summary from PracticalSwift blog:

func shell(_ launchPath: String, _ arguments: [String]) -> String?
{
    let task = Process()
    task.launchPath = launchPath
    task.arguments = arguments

    let pipe = Pipe()
    task.standardOutput = pipe
    task.launch()

    let data = pipe.fileHandleForReading.readDataToEndOfFile()
    let output = String(data: data, encoding: String.Encoding.utf8)

    return output
}

The following Swift code will execute xcodebuild with arguments and then output the result.

shell("xcodebuild", ["-workspace", "myApp.xcworkspace"]);

As for searching the directory contents (which is what ls does in Bash), I suggest using NSFileManager and scanning the directory directly in Swift, instead of Bash output, which can be a pain to parse.

If you don't use command outputs in Swift code, following would be sufficient:

#!/usr/bin/env swift

import Foundation

@discardableResult
func shell(_ args: String...) -> Int32 {
    let task = Process()
    task.launchPath = "/usr/bin/env"
    task.arguments = args
    task.launch()
    task.waitUntilExit()
    return task.terminationStatus
}

shell("ls")
shell("xcodebuild", "-workspace", "myApp.xcworkspace")

Updated: for Swift3/Xcode8