Chaining shell commands with pipe in a Swift script

Question

I'm trying to chain shell command together in a Swift script. The actual commands in question are the output of gource piped to the input of ffmpeg, but here's a simplified, contrived example of what I'm trying to do:

let echo = Process()

echo.launchPath = "/usr/bin/env"
echo.arguments = ["echo", "foo\nbar\nbaz\nbaz", "|", "uniq"]

let pipe = Pipe()
echo.standardOutput = pipe

echo.launch()
echo.waitUntilExit()

// Get the data
let data = pipe.fileHandleForReading.readDataToEndOfFile()
let output = NSString(data: data, encoding: String.Encoding.utf8.rawValue)

print(output ?? "no output")

Expected output:

foo
bar
baz

Actual output:

foo
bar
baz
baz | uniq

The | is being interpreted as part of the last argument. How can I chain commands together, so that data flows from one to the next, in a Swift script? I tried various combinations of assigning standardIn and standardOut and using Pipe() between two Processes, but either I'm doing it wrong, or I'm not connecting the right pieces together.

Answer 1

I got an answer with help from zadr:

import Foundation

let pipe = Pipe()

let echo = Process()
echo.launchPath = "/usr/bin/env"
echo.arguments = ["echo", "foo\nbar\nbaz\nbaz"]
echo.standardOutput = pipe

let uniq = Process()
uniq.launchPath = "/usr/bin/env"
uniq.arguments = ["uniq"]
uniq.standardInput = pipe

let out = Pipe()
uniq.standardOutput = out

echo.launch()
uniq.launch()
uniq.waitUntilExit()

let data = out.fileHandleForReading.readDataToEndOfFile()
let output = NSString(data: data, encoding: String.Encoding.utf8.rawValue)

print(output ?? "no output")