-sed -re '
-s|\b([0-9a-fA-F]{8,40})\b|<a href="./?id=\1">\1</a>|g
-s| #([0-9]+)\b|<a href="http://bugs.example.com/?bug=\1">#\1</a>|g
-'
+# This expression generates links to commits referenced by their SHA1.
+regex=$regex'
+s|\b([0-9a-fA-F]{8,40})\b|<a href="./?id=\1">\1</a>|g'
+# This expression generates links to a fictional bugtracker.
+regex=$regex'
+s| #([0-9]+)\b|<a href="http://bugs.example.com/?bug=\1">#\1</a>|g'
+
+sed -re "$regex"