tty: add missing newline to output

src/uu/tty/src/tty.rs

@@ -33,20 +33,31 @@
     }
 
     let mut stdout = std::io::stdout();
-
     let name = nix::unistd::ttyname(std::io::stdin());
 
     let write_result = match name {
-        Ok(name) => stdout.write_all_os(name.as_os_str()),
+        Ok(name) => {
+            if let Err(e) = stdout.write_all_os(name.as_os_str()) {
+                Err(e)
+            } else if let Err(e) = writeln!(stdout) {
+                Err(e)
+            } else {
+                stdout.flush()
+            }
+        }
         Err(_) => {
             set_exit_code(1);
             writeln!(stdout, "{}", translate!("tty-not-a-tty"))
         }
     };
 
-    if write_result.is_err() || stdout.flush().is_err() {
-        // Don't return to prevent a panic later when another flush is attempted
-        // because the `uucore_procs::main` macro inserts a flush after execution for every utility.
+    if let Err(e) = write_result {
+        eprintln!("tty: write error: {}", e);
+        std::process::exit(3);
+    }
+
+    if let Err(e) = stdout.flush() {
+        eprintln!("tty: write error: {}", e);
         std::process::exit(3);
     }
 

tests/by-util/test_tty.rs

@@ -87,3 +87,44 @@ fn test_stdout_fail() {
     let status = proc.wait().unwrap();
     assert_eq!(status.code(), Some(3));
 }
+
+#[test]
+#[cfg(all(unix, not(target_os = "freebsd")))]
+fn test_newline_in_output() {
+    // Test that output ends with a newline, regardless of success or failure
+    let result = new_ucmd!().run();
+    let stdout = result.stdout_str();
+
+    // Whether it's "not a tty\n" or an actual tty path, it should end with newline
+    assert!(
+        stdout.ends_with('\n'),
+        "Output should end with newline, got: {:?}",
+        stdout
+    );
+}
+
+#[test]
+#[cfg(all(unix, not(target_os = "freebsd")))]
+#[ignore = "Fails on some CI environments - see https://github.com/uutils/coreutils/pull/10252"]
+fn test_write_error_dev_full() {
+    use std::process::{Command, Stdio};
+    use uutests::at_and_ts;
+
+    let (_, ts) = at_and_ts!();
+
+    // Redirect stdout to /dev/full which causes write errors
+    let output = Command::new(ts.bin_path.to_str().unwrap())
+        .arg(&ts.util_name)
+        .stdout(Stdio::from(File::create("/dev/full").unwrap()))
+        .output()
+        .unwrap();
+
+    // Should exit with code 3 and print error to stderr
+    assert_eq!(output.status.code(), Some(3));
+    let stderr = String::from_utf8_lossy(&output.stderr);
+    assert!(
+        stderr.contains("write error"),
+        "Should contain 'write error' in stderr, got: {:?}",
+        stderr
+    );
+}