stdbuf: better handling when non existing files

Should fix tests/misc/stdbuf

src/uu/stdbuf/src/stdbuf.rs

@@ -159,18 +159,26 @@ pub fn uumain(args: impl uucore::Args) -> UResult<()> {
 
     let mut process = match command.spawn() {
         Ok(process) => process,
-        Err(e) if e.kind() == std::io::ErrorKind::PermissionDenied => {
+        Err(e) => match e.kind() {
+            std::io::ErrorKind::PermissionDenied => {
                 return Err(USimpleError::new(
                     126,
                     "failed to execute process: Permission denied",
                 ));
             }
-        Err(e) => {
+            std::io::ErrorKind::NotFound => {
+                return Err(USimpleError::new(
+                    127,
+                    "failed to execute process: No such file or directory",
+                ));
+            }
+            _ => {
                 return Err(USimpleError::new(
                     1,
                     format!("failed to execute process: {}", e),
                 ));
             }
+        },
     };
 
     let status = process.wait().map_err_context(String::new)?;

tests/by-util/test_stdbuf.rs

@@ -20,6 +20,16 @@ fn test_permission() {
         .stderr_contains("Permission denied");
 }
 
+#[test]
+fn test_no_such() {
+    new_ucmd!()
+        .arg("-o1")
+        .arg("no_such")
+        .fails()
+        .code_is(127)
+        .stderr_contains("No such file or directory");
+}
+
 #[cfg(all(not(target_os = "windows"), not(target_os = "openbsd")))]
 #[test]
 fn test_stdbuf_unbuffered_stdout() {