cli: reject invalid pointers with a usage error

When the pointer was omitted, e.g. `jsonpointer a.json b.json`, the first
file was taken as the pointer, every file failed to resolve and the
command still exited with status 0. Validate the pointer before processing
any files and exit with a usage error if it is not a valid JSON pointer.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019xLCiTJTbWQ9Nt7UHq2yiU

Author: claude

bin/jsonpointer

@@ -61,6 +61,13 @@ def parse_pointer(args):
     else:
         parser.error('a JSON pointer is required (POINTER, -p or -f)')
 
+    # Catches e.g. `jsonpointer a.json b.json`, where the pointer was omitted
+    # and the first file would otherwise be used as the pointer
+    try:
+        jsonpointer.JsonPointer(ptr)
+    except jsonpointer.JsonPointerException as e:
+        parser.error('invalid JSON pointer %r: %s' % (ptr, e))
+
     return ptr, files
 
 

tests.py

@@ -529,6 +529,23 @@ def test_no_pointer(self):
         self.assertEqual(proc.returncode, 2)
         self.assertIn('a JSON pointer is required', proc.stderr)
 
+    def test_missing_pointer_multiple_files(self):
+        proc = self._run('a.json', 'b.json')
+        self.assertEqual(proc.returncode, 2)
+        self.assertIn("invalid JSON pointer 'a.json'", proc.stderr)
+        self.assertEqual(proc.stdout, '')
+
+    def test_invalid_pointer_file(self):
+        self._write('bad.txt', 'a\n')
+        proc = self._run('-f', 'bad.txt', 'a.json')
+        self.assertEqual(proc.returncode, 2)
+        self.assertIn("invalid JSON pointer 'a'", proc.stderr)
+
+    def test_empty_pointer(self):
+        proc = self._run('', 'a.json')
+        self.assertEqual(proc.returncode, 0, proc.stderr)
+        self.assertEqual(proc.stdout, '{"a": [1, 2, 3]}\n')
+
     def test_pointer_and_pointer_file_exclusive(self):
         proc = self._run('-p', '/a', '-f', 'ptr.txt', 'a.json')
         self.assertEqual(proc.returncode, 2)