Add example

README.md

@@ -104,7 +104,7 @@ result = reconcile(parent, left, right)
 print(result["text"])  # "Hi beautiful world"
 ```
 
-See the [advanced Python examples](docs/advanced-python.md) for cursor tracking, change provenance, and compact diffs.
+See the [merge-file example](examples/merge_file.py) for a file-merging CLI, or the [advanced examples document](docs/advanced-python.md) for cursor tracking, change provenance, and compact diffs.
 
 ## Motivation
 

docs/advanced-python.md

@@ -86,3 +86,7 @@ assert reconstructed == changed
 ```
 
 Diff entries are positive integers (retain N characters), negative integers (delete N characters), and strings (insert text).
+
+## File Merging Example
+
+For a complete file-merging CLI (a trivial `git merge-file`), see [`examples/merge_file.py`](../examples/merge_file.py).

examples/merge_file.py

@@ -0,0 +1,38 @@
+"""Merge three versions of a file: mine, base, and theirs.
+
+A trivial version of git merge-file (https://git-scm.com/docs/git-merge-file).
+
+Run it with:
+    uv run --directory reconcile-python \
+        python ../examples/merge_file.py my.txt base.txt their.txt [output.txt]
+"""
+
+from __future__ import annotations
+
+import sys
+from pathlib import Path
+
+from reconcile_text import reconcile
+
+
+def main() -> None:
+    args = sys.argv[1:]
+
+    if len(args) < 3 or len(args) > 4:
+        print("Usage: merge_file.py <mine> <base> <theirs> [output]", file=sys.stderr)
+        sys.exit(1)
+
+    mine = Path(args[0]).read_text()
+    base = Path(args[1]).read_text()
+    theirs = Path(args[2]).read_text()
+
+    result = reconcile(base, mine, theirs)
+
+    if len(args) == 4:
+        Path(args[3]).write_text(result["text"])
+    else:
+        print(result["text"], end="")
+
+
+if __name__ == "__main__":
+    main()

reconcile-python/tests/test_reconcile.py

@@ -1,11 +1,14 @@
 from __future__ import annotations
 
+import subprocess
+import sys
 from pathlib import Path
 
 import pytest
 
 from reconcile_text import diff, reconcile, reconcile_with_history, undiff
 
+EXAMPLES_DIR = Path(__file__).resolve().parent.parent.parent / "examples"
 RESOURCES_DIR = Path(__file__).resolve().parent.parent.parent / "tests" / "resources"
 
 FILES = ["pride_and_prejudice.txt", "room_with_a_view.txt", "blns.txt"]
@@ -118,6 +121,50 @@ class TestUndiff:
             undiff("short", [100])
 
 
+class TestExamples:
+    def test_merge_file_stdout(self, tmp_path: Path) -> None:
+        (tmp_path / "base.txt").write_text("Hello world")
+        (tmp_path / "mine.txt").write_text("Hello beautiful world")
+        (tmp_path / "theirs.txt").write_text("Hi world")
+
+        result = subprocess.run(
+            [
+                sys.executable,
+                str(EXAMPLES_DIR / "merge_file.py"),
+                str(tmp_path / "mine.txt"),
+                str(tmp_path / "base.txt"),
+                str(tmp_path / "theirs.txt"),
+            ],
+            capture_output=True,
+            text=True,
+            check=True,
+        )
+
+        assert result.stdout == "Hi beautiful world"
+
+    def test_merge_file_output_file(self, tmp_path: Path) -> None:
+        (tmp_path / "base.txt").write_text("Hello world")
+        (tmp_path / "mine.txt").write_text("Hello beautiful world")
+        (tmp_path / "theirs.txt").write_text("Hi world")
+        output = tmp_path / "output.txt"
+
+        subprocess.run(
+            [
+                sys.executable,
+                str(EXAMPLES_DIR / "merge_file.py"),
+                str(tmp_path / "mine.txt"),
+                str(tmp_path / "base.txt"),
+                str(tmp_path / "theirs.txt"),
+                str(output),
+            ],
+            capture_output=True,
+            text=True,
+            check=True,
+        )
+
+        assert output.read_text() == "Hi beautiful world"
+
+
 class TestDiffUndiffInverse:
     """Verify diff/undiff roundtrip across large real-world texts."""