[s2s] rougeLSum expects \n between sentences (#7410)

Co-authored-by: Swetha Mandava <smandava@nvidia.com>

examples/seq2seq/rouge_cli.py

@@ -0,0 +1,17 @@
+import fire
+
+from utils import calculate_rouge, save_json
+
+
+def calculate_rouge_path(pred_path, tgt_path, save_path=None, **kwargs):
+    """Kwargs will be passed to calculate_rouge"""
+    pred_lns = [x.strip() for x in open(pred_path).readlines()]
+    tgt_lns = [x.strip() for x in open(tgt_path).readlines()][: len(pred_lns)]
+    metrics = calculate_rouge(pred_lns, tgt_lns, **kwargs)
+    if save_path is not None:
+        save_json(metrics, save_path)
+    return metrics  # these print nicely
+
+
+if __name__ == "__main__":
+    fire.Fire(calculate_rouge_path)