[postprocessor:metadata] write to stdout by setting filename to "-"

(#2624)

docs/configuration.rst

@@ -3218,6 +3218,8 @@ Description
     A `format string`_ to build the filenames for metadata files with.
     (see `extractor.filename <extractor.*.filename_>`__)
 
+    Using ``"-"`` as filename will write all output to ``stdout``.
+
     If this option is set, `metadata.extension`_ and
     `metadata.extension-format`_ will be ignored.
 

gallery_dl/postprocessor/metadata.py

@@ -10,6 +10,7 @@
 
 from .common import PostProcessor
 from .. import util, formatter
+import sys
 import os
 
 
@@ -44,8 +45,11 @@ class MetadataPP(PostProcessor):
         filename = options.get("filename")
         extfmt = options.get("extension-format")
         if filename:
-            self._filename = self._filename_custom
-            self._filename_fmt = formatter.parse(filename).format_map
+            if filename == "-":
+                self.run = self._run_stdout
+            else:
+                self._filename = self._filename_custom
+                self._filename_fmt = formatter.parse(filename).format_map
         elif extfmt:
             self._filename = self._filename_extfmt
             self._extension_fmt = formatter.parse(extfmt).format_map
@@ -107,6 +111,9 @@ class MetadataPP(PostProcessor):
             if mtime:
                 util.set_mtime(path, mtime)
 
+    def _run_stdout(self, pathfmt):
+        self.write(sys.stdout, pathfmt.kwdict)
+
     def _directory(self, pathfmt):
         return pathfmt.realdirectory
 

test/test_postprocessor.py

@@ -329,12 +329,22 @@ class MetadataTest(BasePostprocessorTest):
         path = self.pathfmt.realdirectory + "test_file__meta_.data"
         m.assert_called_once_with(path, "w", encoding="utf-8")
 
+    def test_metadata_stdout(self):
+        self._create({"filename": "-", "indent": None})
+
+        with patch("sys.stdout", Mock()) as m:
+            self._trigger()
+
+        self.assertEqual(self._output(m), """\
+{"category": "test", "extension": "ext", "filename": "file"}
+""")
+
     @staticmethod
     def _output(mock):
         return "".join(
             call[1][0]
             for call in mock.mock_calls
-            if call[0] == "().write"
+            if call[0].endswith("write")
         )