* `nix-store --read-log / -l PATH' shows the build log of PATH, if

available.  For instance,

    $ nix-store -l $(which svn) | less

  lets you read the build log of the Subversion instance in your
  profile.

* `nix-store -qb': if applied to a non-derivation, take the deriver.

src/nix-store/help.txt

@@ -9,6 +9,7 @@ Operations:
   --add / -A: copy a path to the Nix store
   --delete: safely delete paths from the Nix store
   --query / -q: query information
+  --read-log / -l: print build log of given store paths
 
   --register-substitutes: register a substitute expression (dangerous!)
   --clear-substitutes: clear all substitutes