diff --git a/src/lib/built_ins.ml b/src/lib/built_ins.ml
--- a/src/lib/built_ins.ml
+++ b/src/lib/built_ins.ml
@@ -87,6 +87,7 @@ params : string list;
 }
 
 type t =
+  | Msh_info
   (* Built-in Actions *)
   | Cd of { path : string option }
   | Pwd
@@ -114,6 +115,7 @@ let reserved = [ "fg"; "bg"; "jobs" ]
 let pp_args = Fmt.(list ~sep:(Fmt.any " ") string)
 
 let to_string = function
+  | Msh_info -> "msh-info"
   | Cd { path = None } -> "cd"
   | Cd { path = Some path } -> Fmt.str "cd %s" path
   | Pwd -> "pwd"
@@ -668,6 +670,7 @@ | "umask" :: _ as cmd -> exec_cmd cmd Umask.t
   | "shift" :: _ as cmd -> exec_cmd cmd Shift.t
   | "read" :: _ as cmd -> exec_cmd cmd Read.t
   | "getopts" :: _ as cmd -> exec_cmd cmd Getopts.t
+  | "msh-info" :: _ -> Some (Ok Msh_info)
   | cmd :: _ ->
       if List.mem cmd reserved then begin
         Debug.Log.err (fun f -> f "Unimplemented built-in: %s" cmd);
diff --git a/src/lib/built_ins.mli b/src/lib/built_ins.mli
--- a/src/lib/built_ins.mli
+++ b/src/lib/built_ins.mli
@@ -46,6 +46,7 @@ params : string list;
 }
 
 type t =
+  | Msh_info (* For debugging the internals of the shell. *)
   | Cd of { path : string option }
       (** Change directory to a path (if [None] then it should be [HOME]) *)
   | Pwd
diff --git a/src/lib/eval.ml b/src/lib/eval.ml
--- a/src/lib/eval.ml
+++ b/src/lib/eval.ml
@@ -130,10 +130,10 @@ | `Double -> Fmt.string ppf "double"
       | `Single -> Fmt.string ppf "single"
     in
     (Fmt.braces
-    @@ Fmt.record
+    @@ Fmt.record ~sep:Fmt.comma
          [
            Fmt.field "quotes" (fun t -> t.quotes) pp_quotes;
-           Fmt.field "rdrs" (fun t -> t.rdrs) Fmt.(lst Types.pp_redirect);
+           Fmt.field "fd-table" (fun t -> t.fd_table) Fd_table.pp;
            Fmt.field "argv" (fun t -> Array.to_list t.argv) Fmt.(lst string);
            Fmt.field "functions"
              (fun t -> t.functions |> List.map fst)
@@ -662,11 +662,30 @@ Fmt.(list Types.pp_redirect)
                                       rdrs);
                                 Eunix.with_redirections ~restore:false rdrs
                                   Fun.id;
+                                let fd_table =
+                                  List.fold_left
+                                    (fun tb -> function
+                                      | Types.Redirect (true, fd, efd, _) ->
+                                          Eio_unix.Fd.use_exn "fd-table-rdr" efd
+                                          @@ fun u ->
+                                          Fd_table.add_fd ~src:fd
+                                            ~tgt:(Obj.magic u : int)
+                                            tb
+                                      | Types.Redirect (false, _, _, _) -> tb
+                                      | Types.Close efd ->
+                                          Eio_unix.Fd.use_exn "fd-table-close"
+                                            efd
+                                          @@ fun u ->
+                                          Fd_table.remove (Obj.magic u : int) tb)
+                                    ctx.fd_table rdrs
+                                in
                                 if args <> [] then
                                   Unix.execve (Option.get prog)
                                     (Array.of_list args)
                                     (get_env ~extra:ctx.local_state ctx)
-                                else job
+                                else
+                                  handle_job job
+                                    (`Rdr (Exit.zero { ctx with fd_table }))
                           | ":" -> job
                           | _ -> (
                               let saved_ctx = ctx in
@@ -1968,7 +1987,11 @@ let rdrs = make_child_rdrs_for_parent rdrs in
     Eunix.with_redirections ~restore:true rdrs @@ fun () ->
     Debug.Log.debug (fun f -> f "built-in: %s" (Built_ins.to_string v));
     match v with
-    | Built_ins.Cd { path } ->
+    | Built_ins.Msh_info ->
+        let str = Fmt.str "msh-info\n%a\n" dump_ctx ctx in
+        Eio.Flow.copy_string str ctx.stdout;
+        Exit.zero ctx
+    | Cd { path } ->
         let cwd = S.cwd ctx.state in
         let+ state =
           match path with
diff --git a/src/lib/fd_table.ml b/src/lib/fd_table.ml
--- a/src/lib/fd_table.ml
+++ b/src/lib/fd_table.ml
@@ -48,3 +48,7 @@ f "FD %i disagreement %a %a" fd pp_resource v1 pp_resource v2);
           Some v2)
 
 let empty = M.empty
+
+let pp ppf t =
+  let bindings = M.bindings t |> List.filter (fun (i, _) -> i > 2) in
+  Fmt.(lst (pair ~sep:(any " -> ") int pp_resource)) ppf bindings
diff --git a/src/lib/fd_table.mli b/src/lib/fd_table.mli
--- a/src/lib/fd_table.mli
+++ b/src/lib/fd_table.mli
@@ -23,3 +23,6 @@ The second FD table takes precedence in the case of conflict. *)
 
 val empty : t
 (** The empty file descriptor table. *)
+
+val pp : t Fmt.t
+(** A pretty printer for FD tables. *)
diff --git a/test/fd_table.t b/test/fd_table.t
new file mode 100644
--- /dev/null
+++ b/test/fd_table.t
@@ -0,0 +1,14 @@
+Keeping track of the file descriptors in-memory (not just the process itself).
+
+  $ cat > test.sh << EOF
+  > exec 4>&1
+  > msh-info
+  > EOF
+
+  $ msh test.sh
+  msh-info
+  {quotes: none,
+            fd-table:
+             [4 -> FD-1, 455 -> Path-pipe:[818672], 456 -> Path-pipe:[818672]],
+            argv: [test.sh],
+            functions: []}