Is there a simple way to write a string to a file descriptor?

Using Swift
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1

Is there a way to write a string to a file descriptor without first opening a file there, for e.g. if the shell has set up the file descriptors for you? An equivalent to GNU libc dprintf, essentially.

2

Here are two options:

1. Using Foundation

import Foundation

let fd: Int32 = 1 // stdout
let message = "Hello world!\n"

let fileHandle = FileHandle(fileDescriptor: fd)
try fileHandle.write(contentsOf: Data(message.utf8))

2. Using Swift System

This requires adding the swift-system library as a dependency to your package.

import SystemPackage

let fd: Int32 = 1 // stdout
let message = "Hello world!\n"

let desc = FileDescriptor(rawValue: fd)
try desc.writeAll(message.utf8)
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3

Aren’t file descriptors unsigned?

4

No. They trace back to C, where a negative return value indicates some error condition.

5

For things like this, which are declared as int in C, I tend to use Swift’s CInt.

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Quinn “The Eskimo!” @ DTS @ Apple

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