Filesystem Operations - Rust By Example
Description: A description

# Filesystem Operations

The `std::fs` module contains several functions that deal with the filesystem.

    use std::fs;
    use std::fs::{File, OpenOptions};
    use std::io;
    use std::io::prelude::*;
    use std::os::unix;
    use std::path::Path;

    // A simple implementation of `% cat path`
    fn cat(path: &Path) -> io::Result<String> {
        let mut f = File::open(path)?;
        let mut s = String::new();
        match f.read_to_string(&mut s) {
            Ok(_) => Ok(s),
            Err(e) => Err(e),
        }
    }

    // A simple implementation of `% echo s > path`
    fn echo(s: &str, path: &Path) -> io::Result<()> {
        let mut f = File::create(path)?;

        f.write_all(s.as_bytes())
    }

    // A simple implementation of `% touch path` (ignores existing files)
    fn touch(path: &Path) -> io::Result<()> {
        match OpenOptions::new().create(true).write(true).open(path) {
            Ok(_) => Ok(()),
            Err(e) => Err(e),
        }
    }

    fn main() {
        println!("`mkdir a`");
        // Create a directory, returns `io::Result<()>`
        match fs::create_dir("a") {
            Err(why) => println!("! {:?}", why.kind()),
            Ok(_) => {},
        }

        println!("`echo hello > a/b.txt`");
        // The previous match can be simplified using the `unwrap_or_else` method
        echo("hello", &Path::new("a/b.txt")).unwrap_or_else(|why| {
            println!("! {:?}", why.kind());
        });

        println!("`mkdir -p a/c/d`");
        // Recursively create a directory, returns `io::Result<()>`
        fs::create_dir_all("a/c/d").unwrap_or_else(|why| {
            println!("! {:?}", why.kind());
        });

        println!("`touch a/c/e.txt`");
        touch(&Path::new("a/c/e.txt")).unwrap_or_else(|why| {
            println!("! {:?}", why.kind());
        });

        println!("`ln -s ../b.txt a/c/b.txt`");
        // Create a symbolic link, returns `io::Result<()>`
        if cfg!(target_family = "unix") {
            unix::fs::symlink("../b.txt", "a/c/b.txt").unwrap_or_else(|why| {
            println!("! {:?}", why.kind());
            });
        }

        println!("`cat a/c/b.txt`");
        match cat(&Path::new("a/c/b.txt")) {
            Err(why) => println!("! {:?}", why.kind()),
            Ok(s) => println!("> {}", s),
        }

        println!("`ls a`");
        // Read the contents of a directory, returns `io::Result<Vec<Path>>`
        match fs::read_dir("a") {
            Err(why) => println!("! {:?}", why.kind()),
            Ok(paths) => for path in paths {
                println!("> {:?}", path.unwrap().path());
            },
        }

        println!("`rm a/c/e.txt`");
        // Remove a file, returns `io::Result<()>`
        fs::remove_file("a/c/e.txt").unwrap_or_else(|why| {
            println!("! {:?}", why.kind());
        });

        println!("`rmdir a/c/d`");
        // Remove an empty directory, returns `io::Result<()>`
        fs::remove_dir("a/c/d").unwrap_or_else(|why| {
            println!("! {:?}", why.kind());
        });
    }

Here's the expected successful output:

    $ rustc fs.rs && ./fs
    `mkdir a`
    `echo hello > a/b.txt`
    `mkdir -p a/c/d`
    `touch a/c/e.txt`
    `ln -s ../b.txt a/c/b.txt`
    `cat a/c/b.txt`
    > hello
    `ls a`
    > "a/b.txt"
    > "a/c"
    `rm a/c/e.txt`
    `rmdir a/c/d`

And the final state of the `a` directory is:

    $ tree a
    a
    |-- b.txt
    `-- c
        `-- b.txt -> ../b.txt

    1 directory, 2 files

An alternative way to define the function `cat` is with `?` notation:

    fn cat(path: &Path) -> io::Result<String> {
        let mut f = File::open(path)?;
        let mut s = String::new();
        f.read_to_string(&mut s)?;
        Ok(s)
    }

### See also:

`cfg!`