tr: use an unbuffered stdout

julian-klode · drinkcat · commit c93b9ed6beb2 · 2025-08-06T15:38:28.000+08:00
Our stdin that we transform already is buffered (using 8192 byte
buffers in the previous commit), so avoid buffering our output
needlessly.

This effectively changes the code to write complete lines
immediately, for example, in

`( echo a; sleep 1 ) | tr a b`

we receive

    read(0, "a\n", 8192)                    = 2
    write(1, "b\n", 2)                      = 2
    read(0, "", 8192)                       = 0

instead of

    read(0, "a\n", 8192)                    = 2
    read(0, "", 8192)                       = 0
    write(1, "b\n", 2)                      = 2

which matches the GNU coreutils behavior.
diff --git a/src/uu/tr/src/tr.rs b/src/uu/tr/src/tr.rs
@@ -12,7 +12,7 @@ use operation::{
     translate_input,
 };
 use std::ffi::OsString;
-use std::io::{BufWriter, Write, stdin, stdout};
+use std::io::{Write, stdin, stdout};
 use uucore::display::Quotable;
 use uucore::error::{FromIo, UResult, USimpleError, UUsageError};
 use uucore::fs::is_stdin_directory;
@@ -107,7 +107,7 @@ pub fn uumain(args: impl uucore::Args) -> UResult<()> {
 
     let stdin = stdin();
     let mut locked_stdin = stdin.lock();
-    let mut buffered_stdout = BufWriter::new(stdout().lock());
+    let mut locked_stdout = stdout().lock();
 
     // According to the man page: translating only happens if deleting or if a second set is given
     let translating = !delete_flag && sets.len() > 1;
@@ -131,34 +131,34 @@ pub fn uumain(args: impl uucore::Args) -> UResult<()> {
             let delete_op = DeleteOperation::new(set1);
             let squeeze_op = SqueezeOperation::new(set2);
             let op = delete_op.chain(squeeze_op);
-            translate_input(&mut locked_stdin, &mut buffered_stdout, op)?;
+            translate_input(&mut locked_stdin, &mut locked_stdout, op)?;
         } else {
             let op = DeleteOperation::new(set1);
-            translate_input(&mut locked_stdin, &mut buffered_stdout, op)?;
+            translate_input(&mut locked_stdin, &mut locked_stdout, op)?;
         }
     } else if squeeze_flag {
         if sets_len == 1 {
             let op = SqueezeOperation::new(set1);
-            translate_input(&mut locked_stdin, &mut buffered_stdout, op)?;
+            translate_input(&mut locked_stdin, &mut locked_stdout, op)?;
         } else {
             let translate_op = TranslateOperation::new(set1, set2.clone())?;
             let squeeze_op = SqueezeOperation::new(set2);
             let op = translate_op.chain(squeeze_op);
-            translate_input(&mut locked_stdin, &mut buffered_stdout, op)?;
+            translate_input(&mut locked_stdin, &mut locked_stdout, op)?;
         }
     } else {
         let op = TranslateOperation::new(set1, set2)?;
-        translate_input(&mut locked_stdin, &mut buffered_stdout, op)?;
+        translate_input(&mut locked_stdin, &mut locked_stdout, op)?;
     }
 
     #[cfg(not(target_os = "windows"))]
-    buffered_stdout
+    locked_stdout
         .flush()
         .map_err_context(|| translate!("tr-error-write-error"))?;
 
     // SIGPIPE is not available on Windows.
     #[cfg(target_os = "windows")]
-    match buffered_stdout.flush() {
+    match locked_stdout.flush() {
         Ok(()) => {}
         Err(err) if err.kind() == std::io::ErrorKind::BrokenPipe => std::process::exit(13),
         Err(err) => return Err(err.map_err_context(|| translate!("tr-error-write-error"))),
