factor: handle the '< .' arg

src/uu/factor/src/cli.rs

@@ -73,11 +73,20 @@ pub fn uumain(args: impl uucore::Args) -> UResult<()> {
         let stdin = stdin();
         let lines = stdin.lock().lines();
         for line in lines {
-            for number in line.unwrap().split_whitespace() {
+            match line {
+                Ok(line) => {
+                    for number in line.split_whitespace() {
                         print_factors_str(number, &mut w, print_exponents)
                             .map_err_context(|| "write error".into())?;
                     }
                 }
+                Err(e) => {
+                    set_exit_code(1);
+                    show_error!("error reading input: {}", e);
+                    return Ok(());
+                }
+            }
+        }
     }
 
     if let Err(e) = w.flush() {

tests/by-util/test_factor.rs

@@ -1258,3 +1258,8 @@ const PRIMES50: &[u64] = &[
     1125899906841623,
     1125899906841613,
 ];
+
+#[test]
+fn fails_on_directory() {
+    new_ucmd!().pipe_in(".").fails();
+}