Applied:
diff -ur a/file1 b/file1
--- a/file1
+++ b/file1
@@ -1,3 +1,3 @@
 context
-file1 here
+modified file1 here
 context

Updated buffer:
diff -ur a/file1 b/file1
--- a/file1
+++ b/file1
@@ -1,3 +1,3 @@
 context
 modified file1 here
 context
-- 
2.43.0