shuf: Treat empty file as zero elements instead of one emptystring

src/uu/shuf/src/shuf.rs

@@ -195,6 +195,13 @@ fn read_input_file(filename: &str) -> UResult<Vec<u8>> {
 }
 
 fn find_seps(data: &mut Vec<&[u8]>, sep: u8) {
+    // Special case: If data is empty (and does not even contain a single 'sep'
+    // to indicate the presence of the empty element), then behave as if the input contained no elements at all.
+    if data.len() == 1 && data[0].is_empty() {
+        data.clear();
+        return;
+    }
+
     // need to use for loop so we don't borrow the vector as we modify it in place
     // basic idea:
     // * We don't care about the order of the result. This lets us slice the slices

tests/by-util/test_shuf.rs

@@ -48,6 +48,13 @@ fn test_zero_termination() {
     assert_eq!(result_seq, input_seq, "Output is not a permutation");
 }
 
+#[test]
+fn test_empty_input() {
+    let result = new_ucmd!().pipe_in(vec![]).succeeds();
+    result.no_stderr();
+    result.no_stdout();
+}
+
 #[test]
 fn test_echo() {
     let input_seq = vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 10];