Shell scripting in Swift, using a proper hashbang and a custom subshell operator.

shell.swift

#!/usr/bin/xcrun swift -i -sdk /Applications/Xcode6-Beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.10.sdk
//
//  shell.swift
//  
//  Shell scripting in Swift, using a proper hashbang and a custom subshell operator.
//  To run: `chmod +x shell.swift && ./shell.swift`.
//
//  If you edit this in Xcode, ignore the error on the hashbang line.
//  To play around with this in a playground, comment out the hashbang line.
//
//  Created by Jeffrey Wear on 6/8/14.
//
//

import Foundation

/**
 Returns the standard output and exit status of running _command_ in a subshell.

 The operator will block (by polling the current run loop) until _command_ exits.

 @param command An absolute path to an executable, optionally followed by one or more arguments.
 @return (output, exitStatus) The output and exit status of the executable invoked
 by _command_.
 */
operator prefix > {}
@prefix func > (command: String) -> (output: String, exitStatus: Int) {
    let tokens = command.componentsSeparatedByString(" ")
    let launchPath = tokens[0]
    let arguments = tokens[1..tokens.count]
    
    let task = NSTask()
    task.launchPath = launchPath
    task.arguments = Array(arguments)
    let stdout = NSPipe.pipe()
    task.standardOutput = stdout
    
    task.launch()
    task.waitUntilExit()
    
    let outData = stdout.fileHandleForReading.readDataToEndOfFile()
    let outStr = NSString(data: outData, encoding: NSUTF8StringEncoding)
    return (outStr, Int(task.terminationStatus))
}

// Note that nothing is printed here;
// '>' captures and returns the output of the command.
assert((>"/bin/echo -n Hello world").exitStatus == 0)

// Now we capture the output.
let command = "/bin/echo -n Hello world"
let (output, exitStatus) = >command
println("'\(command)' exited with status \(exitStatus) and output '\(output)'.")