**Input Validation:** Thoroughly validate user-supplied input to ensure it conforms to the expected format and does
not contain any malicious characters or sequences. Sanitize and normalize file paths to prevent any 
unauthorized navigation.

Example in `Dart`:

```dart
import 'package:file/local.dart';
import 'dart:io';

void main() {
  var fileSystem = LocalFileSystem();
  var currentDirectory = Directory.current.path;
  print(currentDirectory);
  var inputFile = File('$currentDirectory/../../passwords.txt');
  var outputFile = File('$currentDirectory/pass.txt');

  if (!isWithinDirectory(inputFile, currentDirectory) ||
      !isWithinDirectory(outputFile, currentDirectory)) {
    print("Invalid file path");
    return;
  }

  inputFile.copy(outputFile.path)
      .then((_) => print("File copied successfully"))
      .catchError((error) => print("Error: $error"));
}

bool isWithinDirectory(FileSystemEntity file, String directoryPath) {
  var fileDirectory = Directory(file.parent.path);
  var specifiedDirectory = Directory(directoryPath);
  return fileDirectory.path == specifiedDirectory.path ||
      fileDirectory.path.startsWith('${specifiedDirectory.path}${Platform.pathSeparator}');
}


```

Example in `Kotlin`:

```kotlin
import java.io.File

fun readFile(filePath: String): String {
    val sanitizedFilePath = filePath.replace("..", "").replace("/", "")
    val file = File("/var/www/files/$sanitizedFilePath")
    return file.readText()
}

fun main() {
    println("Enter the file name:")
    val fileName = readLine()

    try {
        val content = fileName?.let { readFile(it) }
        println("File content: $content")
    } catch (e: Exception) {
        println("Error: ${e.message}")
    }
}
```

Example in `Swift`:

```swift
import Foundation

func readSensitiveFile(fileURL: URL) -> String? {
    let fileManager = FileManager.default
    
    // Check if the fileURL is within the allowed directory
    if fileURL.pathComponents.contains("path") && fileURL.pathComponents.contains("to") && fileURL.pathComponents.contains("user") {
        let fileContents = fileManager.contents(atPath: fileURL.path)
        return String(data: fileContents!, encoding: .utf8)
    }
    
    return nil
}

func main() {
    let userDirectory = FileManager.default.homeDirectoryForCurrentUser
    let userInput = "/path/to/user/input.txt"
    let fileURL = userDirectory.appendingPathComponent(userInput)
    
    if let contents = readSensitiveFile(fileURL: fileURL) {
        print("File contents: \(contents)")
    } else {
        print("Failed to read file.")
    }
}

main()

```

**Absolute Path Usage:** Prefer using absolute paths instead of relative paths whenever possible. By using absolute paths, the application explicitly specifies the exact location of the file or directory, leaving no room for interpretation.

Example in `Dart`:

```dart
import 'dart:io';
import 'package:path/path.dart' as path;

void main() {
  final absolutePath = '/path/to/file.txt';
  var file = File(absolutePath);
  
  // print('File name: ${path.basename(dir.file.path)}');
  print('File name: ${path.basename(file.path)}');
}
```

Example in `Kotlin`:

```kotlin
import java.io.File

fun main() {
    val absolutePath = "/path/to/file.txt"
    val file = File(absolutePath)

    if (file.exists()) {
        // Perform operations on the file
        println("File exists at $absolutePath")
    } else {
        println("File not found at $absolutePath")
    }
}

```

Example in `Swift`:

```swift
import Foundation

func main() {
    let absolutePath = "/path/to/file.txt"
    let fileManager = FileManager.default

    if fileManager.fileExists(atPath: absolutePath) {
        // Perform operations on the file
        print("File exists at \(absolutePath)")
    } else {
        print("File not found at \(absolutePath)")
    }
}

main()

```
