Swift FileManager usage

file.swift

import Foundation

@main struct FileScratch {
    static func main() {
        let fm: FileManager = .default
        let home: URL = fm.homeDirectoryForCurrentUser
        // Older API for `.appending(path:directoryHint:)`: `.appendingPathComponent(_:)`
        // https://developer.apple.com/documentation/foundation/url/1780239-appendingpathcomponent
        let outputFile = home
            .appending(path: "Desktop")
            .appending(path: "tmp")
            .appending(path: "output.txt")
        let outputDir = outputFile.deletingLastPathComponent()

        if !fm.directoryExists(at: outputDir.path(percentEncoded: false)) {
            try? fm.createDirectory(at: outputDir, withIntermediateDirectories: true)
        }
        if !fm.fileExists(atPath: outputFile.path(percentEncoded: false)) {
            fm.createFile(atPath: outputFile.path(percentEncoded: false), contents: nil)
        }

        guard let outputFileHandle = try? FileHandle(forUpdating: outputFile) else {
            print("cannot open file at \(outputFile.path(percentEncoded: false))")
            return
        }
        defer { try? outputFileHandle.close() }

        // try? outputFileHandle.truncate(atOffset: 0) // <-- clear all
        _ = try? outputFileHandle.seekToEnd() // <-- move cursor to end

        try? outputFileHandle.write(contentsOf: "text".data(using: .utf8)!)
        try? outputFileHandle.write(contentsOf: "\n".data(using: .utf8)!)

        try? outputFileHandle.synchronize() // <-- flush

        try? outputFileHandle.write(contentsOf: "end".data(using: .utf8)!)
    }
}

private extension FileManager {
    func directoryExists(at path: String) -> Bool {
        var isDirectory: ObjCBool = false
        let exists = self.fileExists(atPath: path, isDirectory: &isDirectory)
        return exists && isDirectory.boolValue
    }
}