Paths and the file system

First review the working directory, terminal, and errors. We only build a path here; no file is created.

Familiar image and recall map

An address on an envelope says where to look for a house; it does not promise that the house exists or its door is open. A path is an address for a file or folder. The current working directory is the location from which a program resolves a relative path. The image has a limit: the same relative path can lead to different places when run from different directories.

Path — borrowed path view → join — add a name → PathBuf — owned path → check before acting. Path::new("data") makes a borrowed path view; PathBuf owns the joined path. join("tasks.txt") adds a component according to the operating system’s rules. std::path::{Path, PathBuf} imports two names from one module; the braces group the names. is_absolute() tells whether the address starts at a root; data/tasks.txt is relative. file_name() returns Option because a root or unusual path can lack a final name. This teaching example certainly has one, so unwrap() is appropriate; handle None for a user supplied path. to_string_lossy() displays an OS file name as text, potentially replacing characters that are not valid UTF-8; keep Path or PathBuf for actual file operations.

Build an address without touching the disk

use std::path::{Path, PathBuf};

fn main() {
    let folder = Path::new("data");
    let file: PathBuf = folder.join("tasks.txt");
    println!("{}", file.is_absolute());
    println!("{}", file.file_name().unwrap().to_string_lossy());
}

false
tasks.txt

false means relative; the final line is the file name. We avoid printing the whole path because directory separators differ between Windows and Unix. Paths can contain spaces and Kazakh letters; join avoids writing a separator yourself.

The file operation checks access permissions: an existing path can still yield PermissionDenied. A correct address does not open a locked door.

Recall without looking

1. From where is data/tasks.txt resolved?
2. How do PathBuf and Path differ?
3. Does a well-formed path prove that a file exists?

Exercise

Required. Add a second path folder.join("backup.txt") and print only its name, backup.txt. Then run the project from another working directory with cargo run --manifest-path PATH_TO_PROJECT/Cargo.toml: --manifest-path locates the Cargo project; cargo run keeps the terminal’s current working directory for the program. Explain where the relative path would now resolve. Create no files and use no real personal data path.

Answers

use std::path::{Path, PathBuf};

fn main() {
    let folder = Path::new("data");
    let file: PathBuf = folder.join("tasks.txt");
    println!("{}", file.is_absolute());
    println!("{}", file.file_name().unwrap().to_string_lossy());
    let backup = folder.join("backup.txt");
    println!("{}", backup.file_name().unwrap().to_string_lossy());
}

false
tasks.txt
backup.txt

After checking

Choose a real data location explicitly and show it to the user. The next lesson treats missing and inaccessible files as input/output results. If working directories remain unclear, revisit lesson 4. Official PathBuf documentation.

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