Module 18: File Operations

Practice Tasks

Complete these tasks to reinforce what you learned in this module.

Task 1: Read and print

In main, use std::fs::read_to_string to read a file path given as the first command-line argument (std::env::args().nth(1)). If no path is given, print a short usage message and exit. If read succeeds, print the contents; on error, print the error with eprintln!.

Expected Output:

Running `cargo run -p course_18_file_operations --bin task_01 -- README.md` (or any existing file) prints that file’s contents. Running without args prints usage.

Hint: Get the first argument from std::env::args(); if missing, print usage and exit. Use fs::read_to_string and handle the Result (e.g. with match).

Starter Code:

task.rs

// Task 1: Read file from CLI arg and print. See tasks/TASKS.md.

fn main() {
    todo!("Read path from args, read_to_string, print or usage/error");
}

Task 2: Write a line count

Read a file path from the first CLI argument. Read the file, count the number of lines (split by \n), and write the result to a new file line_count.txt as a single line (e.g. lines: 42). Use fs::read_to_string and fs::write. Handle missing path and I/O errors.

Expected Output:

After running with an existing file, `line_count.txt` exists and contains e.g. `lines: 10` (depending on the file).

Hint: Read the file into a string, then use a method that gives you lines (and count them). Write the count to a file with fs::write; you can use format! for the content.

Starter Code:

task.rs

// Task 2: Line count and write to file. See tasks/TASKS.md.

fn main() {
    todo!("Read file from arg, count lines, write to line_count.txt");
}