gh-93096: Update and document pickle CLI

Doc/library/cmdline.rst

@@ -26,7 +26,7 @@ The following modules have a command-line interface.
 * :ref:`json <json-commandline>`
 * :mod:`mimetypes`
 * :mod:`pdb`
-* :mod:`pickle`
+* :ref:`pickle <pickle-cli>`
 * :ref:`pickletools <pickletools-cli>`
 * :mod:`platform`
 * :mod:`poplib`

Doc/library/pickle.rst

@@ -511,6 +511,35 @@ The :mod:`pickle` module exports three classes, :class:`Pickler`,
       Release the underlying buffer exposed by the PickleBuffer object.
 
 
+.. _pickle-cli:
+
+Command-line interface
+----------------------
+
+The :mod:`pickle` module can be invoked as a script from the command line,
+it will display contents of the pickle files. However, when the pickle file
+that you want to examine comes from an untrusted source, ``-m pickletools``
+is a safer option because it does not execute pickle bytecode, see
+:ref:`pickletools CLI usage <pickletools-cli>`.
+
+.. code-block:: bash
+
+   python -m pickle pickle_file [pickle_file ...]
+
+The following option is accepted:
+
+.. program:: pickle
+
+.. option:: pickle_file
+
+   A pickle file, which can be a regular filename or a filepath.
+   Additionally, you can use ``-`` to read from standard input (stdin).
+   For example, you can pipe a pickle file to the script using a command like:
+
+   .. code-block:: bash
+      echo ... | python -m pickle -
+
+
 .. _pickle-picklable:
 
 What can be pickled and unpickled?

Lib/pickle.py

@@ -1909,20 +1909,17 @@ def _loads(s, /, *, fix_imports=True, encoding="ASCII", errors="strict",
 
 if __name__ == "__main__":
     import argparse
+    import pprint
     parser = argparse.ArgumentParser(
         description='display contents of the pickle files')
     parser.add_argument(
         'pickle_file',
-        nargs='*', help='the pickle file')
+        nargs='+', help='the pickle file')
     args = parser.parse_args()
-    if not args.pickle_file:
-        parser.print_help()
-    else:
-        import pprint
-        for fn in args.pickle_file:
-            if fn == '-':
-                obj = load(sys.stdin.buffer)
-            else:
-                with open(fn, 'rb') as f:
-                    obj = load(f)
-            pprint.pprint(obj)
+    for fn in args.pickle_file:
+        if fn == '-':
+            obj = load(sys.stdin.buffer)
+        else:
+            with open(fn, 'rb') as f:
+                obj = load(f)
+        pprint.pprint(obj)