test.txt

james@archx1c6g ➜  write-test git:(master) ✗ cat ./src/main.rs
use std::io::Write;

fn main() {
    for _ in 0..10 {
        writeln!(
            ::std::io::stdout().lock(),
            "Hello, world!"
        ).unwrap_or_else(|_| {
            eprintln!("stderr: Hello, stderr!");
        });
        // This panics
        // println!("Hello, world!");
        ::std::thread::sleep_ms(1000);
    }

    eprintln!("stderr: Test Over in Rust!");
}
james@archx1c6g ➜  write-test git:(master) ✗ cat ./test.sh
set -euxo pipefail

cargo build

./target/debug/write-test | head -n 5

echo "Test Passed!"
james@archx1c6g ➜  write-test git:(master) ✗ ./test.sh
+ cargo build
   Compiling write-test v0.1.0 (/tmp/write-test)
warning: use of deprecated item 'std::thread::sleep_ms': replaced by `std::thread::sleep`
  --> src/main.rs:13:9
   |
13 |         ::std::thread::sleep_ms(1000);
   |         ^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: `#[warn(deprecated)]` on by default

    Finished dev [unoptimized + debuginfo] target(s) in 0.22s
+ ./target/debug/write-test
+ head -n 5
Hello, world!
Hello, world!
Hello, world!
Hello, world!
Hello, world!
stderr: Hello, stderr!
stderr: Hello, stderr!
stderr: Hello, stderr!
stderr: Hello, stderr!
stderr: Test Over in Rust!
+ echo 'Test Passed!'
Test Passed!
james@archx1c6g ➜  write-test git:(master) ✗