Вот несколько способов записи строки в файл на различных языках программирования:

1. Python:

   string = "Hello, world!"
   with open("filename.txt", "w") as file:
   file.write(string)

2. Java:

   import java.io.FileWriter;
   import java.io.IOException;
   public class Main {
   public static void main(String[] args) {
       String string = "Hello, world!";
       try {
           FileWriter fileWriter = new FileWriter("filename.txt");
           fileWriter.write(string);
           fileWriter.close();
       } catch (IOException e) {
           e.printStackTrace();
       }
   }
   }

3. C++:

   #include <iostream>
   #include <fstream>
   using namespace std;
   int main() {
   string str = "Hello, world!";
   ofstream file("filename.txt");
   if (file.is_open()) {
       file << str;
       file.close();
   }
   return 0;
   }

4. JavaScript (Node.js):

   const fs = require('fs');
   const string = "Hello, world!";
   fs.writeFile('filename.txt', string, (err) => {
   if (err) throw err;
   console.log('File written!');
   });