diff --git a/bin/mechanicaldiff.py b/bin/mechanicaldiff.py
index 6a6166c..eac2c4f 100755
--- a/bin/mechanicaldiff.py
+++ b/bin/mechanicaldiff.py
@@ -3,11 +3,17 @@
 import sys
 
 
-def should_include_hunk(hunk_text: str) -> bool:
+def should_include_hunk(hunk_text: str, search: str, replace: str) -> bool:
     return True
 
 
 def main() -> None:
+    if len(sys.argv) != 3:
+        raise SystemExit("Usage: mechanicaldiff <search> <replace>")
+
+    search = sys.argv[1]
+    replace = sys.argv[2]
+
     lines = sys.stdin.read().splitlines(keepends=True)
     preamble_lines = []
     sections = []
@@ -46,7 +52,7 @@ def main() -> None:
         kept_hunks = []
         for hunk_lines in section["hunks"]:
             hunk_text = "".join(hunk_lines)
-            if should_include_hunk(hunk_text):
+            if should_include_hunk(hunk_text, search, replace):
                 kept_hunks.append(hunk_lines)
 
         if not kept_hunks: