diff --git a/bin/dune b/bin/dune
new file mode 100644
index 0000000..62e6447
--- /dev/null
+++ b/bin/dune
@@ -0,0 +1,3 @@
+(executable
+ (name meowc)
+ (libraries meow unix))
diff --git a/bin/meowc.ml b/bin/meowc.ml
new file mode 100644
index 0000000..762a63f
--- /dev/null
+++ b/bin/meowc.ml
@@ -0,0 +1,466 @@
+open Meow
+open Types
+
+let usage =
+  String.concat "\n"
+    [
+      Style.bold "meowc" ^ Style.dim "  a build tool for C and C++";
+      "";
+      Style.bold "  usage";
+      "    meowc [build] [target...]     build everything, or the named targets";
+      "    meowc run <bin> [args...]     build a bin target, then run it";
+      "    meowc test [filter]           build and run test targets";
+      "    meowc install                 copy installable outputs under the prefix";
+      "    meowc configure               run the checks and write the config header";
+      "    meowc check                   parse and validate, build nothing";
+      "    meowc targets                 list every target";
+      "    meowc graph [--dot]           show the dependency graph";
+      "    meowc explain <file>          say why a file is or is not up to date";
+      "    meowc compdb                  write compile_commands.json";
+      "    meowc watch [target...]       rebuild whenever an input changes";
+      "    meowc init <name>             scaffold a new project here";
+      "    meowc clean                   delete the build directory";
+      "";
+      Style.bold "  options";
+      "    -f FILE        build file to read (default build.meow)";
+      "    -j N           parallel jobs (default: cores)";
+      "    -C DIR         change to DIR first";
+      "    -D name=value  set an option declared with 'option'";
+      "    --prefix DIR   install prefix (default /usr/local)";
+      "    -k             keep going after a failure";
+      "    -n             dry run, print what would happen";
+      "    -v             print each command as it finishes";
+      "    -q             only print warnings and errors";
+      "    --no-color     plain output";
+    ]
+
+let cores () =
+  match Fs.read "/proc/cpuinfo" with
+  | exception Sys_error _ -> 4
+  | s ->
+      max 1
+        (List.length
+           (List.filter
+              (fun l -> String.length l >= 9 && String.sub l 0 9 = "processor")
+              (String.split_on_char '\n' s)))
+
+let duration s = if s >= 1.0 then Printf.sprintf "%.2f s" s else Printf.sprintf "%.0f ms" (s *. 1000.0)
+
+type flags = {
+  mutable file : string;
+  mutable jobs : int;
+  mutable chdir : string;
+  mutable defs : (string * string) list;
+  mutable prefix : string option;
+  mutable keep : bool;
+  mutable dry : bool;
+  mutable verbose : bool;
+  mutable quiet : bool;
+  mutable dot : bool;
+  mutable targets_only : bool;
+  mutable interval : float;
+}
+
+let fl =
+  { file = "build.meow"; jobs = 0; chdir = ""; defs = []; prefix = None; keep = false;
+    dry = false; verbose = false; quiet = false; dot = false; targets_only = false;
+    interval = 0.25 }
+
+let parse_args argv =
+  let rest = ref [] in
+  (* Once "run <target>" is on the positional list, the rest belongs to the
+     program being run, not to meowc. "--" ends option parsing anywhere. *)
+  let passthrough () = match !rest with "run" :: _ :: _ -> true | _ -> false in
+  let rec go = function
+    | [] -> ()
+    | "--" :: r when passthrough () -> rest := !rest @ r
+    | args when passthrough () -> rest := !rest @ args
+    | "--" :: r -> rest := !rest @ r
+    | "-f" :: v :: r -> fl.file <- v; go r
+    | "-j" :: v :: r ->
+        fl.jobs <- (try int_of_string v with _ -> Diag.error "-j wants a number, got %S" v);
+        go r
+    | "-C" :: v :: r -> fl.chdir <- v; go r
+    | "-D" :: v :: r ->
+        (match String.index_opt v '=' with
+        | None -> Diag.error ~hint:"write -D name=value" "malformed -D %S" v
+        | Some i ->
+            fl.defs <- fl.defs @ [ (String.sub v 0 i, String.sub v (i + 1) (String.length v - i - 1)) ]);
+        go r
+    | "--prefix" :: v :: r -> fl.prefix <- Some v; go r
+    | "--interval" :: v :: r -> fl.interval <- (try float_of_string v with _ -> 0.25); go r
+    | "--dot" :: r -> fl.dot <- true; go r
+    | "--targets" :: r -> fl.targets_only <- true; go r
+    | "-k" :: r -> fl.keep <- true; go r
+    | "-n" :: r -> fl.dry <- true; go r
+    | "-v" :: r -> fl.verbose <- true; go r
+    | "-q" :: r -> fl.quiet <- true; go r
+    | "--no-color" :: r -> Style.enabled := false; go r
+    | ("-h" | "--help") :: _ -> print_endline usage; exit 0
+    | (("-f" | "-j" | "-C" | "-D" | "--prefix") as o) :: [] -> Diag.error "%s needs a value" o
+    | a :: r when String.length a > 2 && String.sub a 0 2 = "-j" ->
+        let v = String.sub a 2 (String.length a - 2) in
+        fl.jobs <- (try int_of_string v with _ -> Diag.error "-j wants a number, got %S" v);
+        go r
+    | a :: r when String.length a > 2 && String.sub a 0 2 = "-D" ->
+        go ("-D" :: String.sub a 2 (String.length a - 2) :: r)
+    | a :: r when String.length a > 2 && String.sub a 0 2 = "-f" ->
+        fl.file <- String.sub a 2 (String.length a - 2);
+        go r
+    | a :: r when String.length a > 2 && String.sub a 0 2 = "-C" ->
+        fl.chdir <- String.sub a 2 (String.length a - 2);
+        go r
+    | a :: _ when String.length a > 1 && a.[0] = '-' ->
+        Diag.error ~hint:"run 'meowc --help' for the full list" "unknown option %s" a
+    | a :: r -> rest := !rest @ [ a ]; go r
+  in
+  go argv;
+  !rest
+
+let banner p =
+  if not fl.quiet then begin
+    Printf.printf "%s  %s%s\n\n" (Style.bold "meowc")
+      (Style.pad 40 (Style.dim fl.file))
+      (Style.dim p.pname);
+    flush stdout
+  end
+
+let configure () =
+  if not (Sys.file_exists fl.file) then
+    Diag.error ~hint:"run 'meowc init <name>' to start one" "no %s here" fl.file;
+  let overrides = Hashtbl.create 8 in
+  List.iter (fun (k, v) -> Hashtbl.replace overrides k v) fl.defs;
+  let env = Eval.create ~overrides ~quiet:fl.quiet ~builddir:"build" in
+  (match fl.prefix with Some p -> Eval.setvar env "prefix" [ p ] | None -> ());
+  let stmts = Parse.file fl.file in
+  Eval.run env (Filename.dirname fl.file) stmts;
+  env.Eval.probe.Probe.path <- Filename.concat env.Eval.tc.builddir ".meowc-probe";
+  Fs.mkdir_p env.Eval.tc.builddir;
+  Probe.save env.Eval.probe;
+  List.iter
+    (fun (k, _) ->
+      if not (Hashtbl.mem env.Eval.opts k) then
+        Diag.error ~hint:"only options declared with 'option' can be set" "no option named %S" k)
+    fl.defs;
+  let p = Resolve.project env in
+  if env.Eval.probes_shown > 0 && not fl.quiet then print_newline ();
+  p
+
+let with_config_header p =
+  match Configh.emit p with
+  | Some (path, true) when not fl.quiet ->
+      Printf.printf "  %s%s\n" (Style.yellow (Style.pad 8 "config")) path
+  | _ -> ()
+
+let unknown_target p name =
+  Diag.error
+    ~hint:(Suggest.hint name (List.map (fun (t : target) -> t.name) p.targets))
+    "no target named %S" name
+
+let select_targets p names =
+  match names with
+  | [] -> List.filter (fun (t : target) -> t.kind <> Test) p.targets
+  | _ -> List.map (fun n -> match find p n with Some t -> t | None -> unknown_target p n) names
+
+let on_start (n : Graph.node) =
+  if fl.dry then Printf.printf "  %s%s\n" (Build.paint n.tag (Style.pad 8 n.tag)) n.label
+
+let on_done ~ok ~log (n : Graph.node) =
+  if ok then Printf.printf "  %s%s\n" (Build.paint n.tag (Style.pad 8 n.tag)) n.label
+  else
+    Printf.printf "  %s%s\n%s\n" (Style.red (Style.pad 8 "failed")) n.label
+      (Style.dim ("      " ^ Exec.show n.cmd));
+  if String.trim log <> "" then (print_string log; flush stdout);
+  flush stdout
+
+let execute p ~names =
+  let b = Build.of_project p in
+  let targets = select_targets p names in
+  let selected = Build.select b targets in
+  let jobs = if fl.jobs > 0 then fl.jobs else cores () in
+  if fl.dry then begin
+    let order = Graph.topo b.g in
+    let n = ref 0 in
+    List.iter
+      (fun i ->
+        if Hashtbl.mem selected i then begin
+          let v = b.g.Graph.nodes.(i) in
+          incr n;
+          Printf.printf "  %s%s\n" (Build.paint v.tag (Style.pad 8 v.tag)) v.label;
+          if fl.verbose then print_endline ("      " ^ Style.dim (Exec.show v.cmd))
+        end)
+      order;
+    Printf.printf "\n  %s\n" (Style.dim (Printf.sprintf "%d actions, nothing run" !n));
+    (b, { Sched.built = 0; cached = 0; failed = 0 })
+  end
+  else begin
+    let cache = Cache.load (Filename.concat p.tc.builddir ".meowc-cache") in
+    ignore (Graph.topo b.g);
+    let r =
+      Fun.protect
+        ~finally:(fun () -> Cache.save cache)
+        (fun () ->
+          Sched.run b.g ~selected ~jobs ~cache ~verbose:fl.verbose ~keep_going:fl.keep ~on_start
+            ~on_done)
+    in
+    (b, r)
+  end
+
+let summarise (r : Sched.result) elapsed =
+  if not fl.quiet && not fl.dry then begin
+    let text =
+      if r.failed > 0 then Style.red (Style.plural r.failed "action" ^ " failed")
+      else if r.built = 0 then Style.dim "nothing to do"
+      else Printf.sprintf "%d built%s" r.built (Style.dim (Printf.sprintf ", %d cached" r.cached))
+    in
+    Printf.printf "%s  %s%s\n"
+      (if r.built + r.failed = 0 then "" else "\n")
+      (Style.pad 48 text) (Style.dim (duration elapsed))
+  end;
+  if r.failed > 0 then exit 1
+
+let cmd_build names =
+  let p = configure () in
+  banner p;
+  with_config_header p;
+  let t0 = Unix.gettimeofday () in
+  let _, r = execute p ~names in
+  summarise r (Unix.gettimeofday () -. t0);
+  p
+
+let cmd_run = function
+  | [] -> Diag.error ~hint:"try: meowc run <bin>" "run needs a target name"
+  | name :: args ->
+      let p = configure () in
+      let t = match find p name with
+        | Some ({ kind = Bin; _ } as t) -> t
+        | Some t -> Diag.error "%s is a %s, not a bin" name (kind_name t.kind)
+        | None -> unknown_target p name
+      in
+      banner p;
+      with_config_header p;
+      let t0 = Unix.gettimeofday () in
+      let _, r = execute p ~names:[ name ] in
+      summarise r (Unix.gettimeofday () -. t0);
+      let exe = Build.bin_of p t in
+      if not fl.quiet then Printf.printf "\n  %s\n" (Style.dim exe);
+      flush stdout;
+      Unix.execv exe (Array.of_list (exe :: args))
+
+let cmd_test filter =
+  let p = configure () in
+  banner p;
+  with_config_header p;
+  let all = Testrun.tests p in
+  let chosen =
+    match filter with
+    | [] -> all
+    | fs -> List.filter (fun (t : target) -> List.exists (fun f -> Glob.matches f t.name) fs) all
+  in
+  if chosen = [] then begin
+    Printf.printf "  %s\n" (Style.dim "no test targets");
+    exit 0
+  end;
+  let t0 = Unix.gettimeofday () in
+  let _, r = execute p ~names:(List.map (fun (t : target) -> t.name) chosen) in
+  if r.failed > 0 then summarise r (Unix.gettimeofday () -. t0);
+  if r.built > 0 then print_newline ();
+  let results = List.map (Testrun.run_one p) chosen in
+  List.iter
+    (fun (o : Testrun.outcome) ->
+      Printf.printf "  %s%s%s\n"
+        (if o.ok then Style.green (Style.pad 8 "pass") else Style.red (Style.pad 8 "fail"))
+        (Style.pad 40 o.name)
+        (Style.dim (Printf.sprintf "%.0f ms" o.ms));
+      if not o.ok then begin
+        print_string o.output;
+        Printf.printf "  %s\n" (Style.dim (Printf.sprintf "exit %d" o.code))
+      end)
+    results;
+  let passed = List.length (List.filter (fun (o : Testrun.outcome) -> o.ok) results) in
+  let total = List.length results in
+  let text =
+    if passed = total then Style.green (Printf.sprintf "%d of %d passed" passed total)
+    else Style.red (Printf.sprintf "%d of %d passed" passed total)
+  in
+  Printf.printf "\n  %s%s\n" (Style.pad 48 text)
+    (Style.dim (duration (Unix.gettimeofday () -. t0)));
+  if passed <> total then exit 1
+
+let cmd_install () =
+  let p = cmd_build [] in
+  let items = Install.execute ~dry:fl.dry p in
+  print_newline ();
+  List.iter
+    (fun (src, dst) ->
+      Printf.printf "  %s%s %s %s\n"
+        (Style.green (Style.pad 8 (if fl.dry then "would" else "install")))
+        (Style.pad 30 (Filename.basename src)) (Style.dim "->") (Style.dim dst))
+    items;
+  if items = [] then Printf.printf "  %s\n" (Style.dim "nothing is marked for installation")
+  else Printf.printf "\n  %s\n" (Style.dim (Style.plural (List.length items) "file" ^ " under " ^ p.prefix))
+
+let cmd_targets () =
+  let p = configure () in
+  banner p;
+  List.iter
+    (fun (t : target) ->
+      let tag, paint = Build.tag_of t.kind in
+      ignore tag;
+      Printf.printf "  %s%s%s%s\n"
+        (paint (Style.pad 9 (kind_name t.kind)))
+        (Style.pad 22 t.name)
+        (Style.pad 20 (Style.dim (Style.plural (List.length (all_srcs t)) "source")))
+        (Style.dim (if t.uses = [] then "" else "uses " ^ String.concat " " t.uses)))
+    p.targets;
+  Printf.printf "\n  %s\n" (Style.dim (Style.plural (List.length p.targets) "target"))
+
+let cmd_graph () =
+  let p = configure () in
+  if fl.targets_only then print_string (Dot.targets_only p)
+  else
+    let b = Build.of_project p in
+    if fl.dot then print_string (Dot.render b)
+    else begin
+      banner p;
+      let order = Graph.topo b.g in
+      List.iter
+        (fun i ->
+          let v = b.g.Graph.nodes.(i) in
+          Printf.printf "  %s%s\n" (Build.paint v.tag (Style.pad 8 v.tag)) (Style.pad 34 v.label);
+          List.iter
+            (fun d -> Printf.printf "      %s %s\n" (Style.dim "<-") (Style.dim b.g.Graph.nodes.(d).label))
+            v.deps)
+        order;
+      Printf.printf "\n  %s\n"
+        (Style.dim (Style.plural (Array.length b.g.Graph.nodes) "action"))
+    end
+
+let cmd_explain = function
+  | [] -> Diag.error "explain needs a file path"
+  | path :: _ ->
+      let p = configure () in
+      let b = Build.of_project p in
+      banner p;
+      (match Graph.producing b.g path with
+      | None ->
+          Printf.printf "  %s is not produced by this build\n" (Style.bold path);
+          let users =
+            Array.to_list b.g.Graph.nodes
+            |> List.filter (fun (n : Graph.node) -> List.mem path (Sched.inputs_of n))
+          in
+          if users <> [] then begin
+            Printf.printf "  %s\n" (Style.dim "it is an input to:");
+            List.iter (fun (n : Graph.node) -> Printf.printf "      %s %s\n" (Build.paint n.tag n.tag) n.label) users
+          end
+      | Some i ->
+          let n = b.g.Graph.nodes.(i) in
+          let cache = Cache.load (Filename.concat p.tc.builddir ".meowc-cache") in
+          let fresh = Sched.up_to_date cache n in
+          Printf.printf "  %s%s\n" (Build.paint n.tag (Style.pad 8 n.tag)) (Style.bold n.label);
+          Printf.printf "      %s %s\n" (Style.dim "command") (Style.dim (Exec.show n.cmd));
+          Printf.printf "      %s %s\n" (Style.dim "state  ")
+            (if fresh then Style.green "up to date" else Style.yellow "will rebuild");
+          if not fresh then begin
+            if not (List.for_all Sys.file_exists n.outs) then
+              Printf.printf "      %s %s\n" (Style.dim "reason ") "output is missing"
+            else if Cache.current cache (List.hd n.outs) = None then
+              Printf.printf "      %s %s\n" (Style.dim "reason ") "no cached key for this output"
+            else Printf.printf "      %s %s\n" (Style.dim "reason ") "an input or the command changed"
+          end;
+          Printf.printf "      %s\n" (Style.dim "inputs");
+          List.iter
+            (fun i ->
+              let d = match Cache.digest_file i with Some d -> String.sub d 0 8 | None -> "missing " in
+              Printf.printf "        %s  %s\n" (Style.dim d) i)
+            (Sched.inputs_of n))
+
+let cmd_compdb () =
+  let p = configure () in
+  let b = Build.of_project p in
+  let path = "compile_commands.json" in
+  let n = Compdb.write b path in
+  Printf.printf "  %s%s %s\n" (Style.green (Style.pad 8 "wrote")) path
+    (Style.dim (Style.plural n "entry"))
+
+let cmd_watch names =
+  let round () =
+    let p = configure () in
+    with_config_header p;
+    let t0 = Unix.gettimeofday () in
+    let b, r = execute p ~names in
+    summarise r (Unix.gettimeofday () -. t0);
+    b
+  in
+  let rec loop () =
+    let b = (try Some (round ()) with Diag.Stop ds -> Diag.print ds; None) in
+    let files = match b with Some b -> Watch.inputs b | None -> [ fl.file ] in
+    let files = if List.mem fl.file files then files else fl.file :: files in
+    Printf.printf "\n  %s %s\n" (Style.dim "watching") (Style.dim (Style.plural (List.length files) "file"));
+    flush stdout;
+    let changed = Watch.wait ~interval:fl.interval files in
+    Printf.printf "\n  %s %s\n\n" (Style.yellow "changed") (String.concat " " (List.map Filename.basename changed));
+    flush stdout;
+    loop ()
+  in
+  loop ()
+
+let cmd_clean () =
+  let p = configure () in
+  if Sys.file_exists p.tc.builddir then begin
+    Fs.rm_rf p.tc.builddir;
+    Printf.printf "  %s%s\n" (Style.dim (Style.pad 8 "removed")) p.tc.builddir
+  end
+  else Printf.printf "  %s\n" (Style.dim "already clean")
+
+let cmd_init = function
+  | [] -> Diag.error ~hint:"try: meowc init hello" "init needs a project name"
+  | name :: _ ->
+      let files = Scaffold.create name in
+      Printf.printf "  %s %s\n\n" (Style.bold "meowc") (Style.dim ("new project " ^ name));
+      List.iter (fun f -> Printf.printf "  %s%s\n" (Style.green (Style.pad 8 "new")) f) files;
+      Printf.printf "\n  %s\n" (Style.dim "now run: meowc run " ^ name)
+
+let cmd_check () =
+  let p = configure () in
+  banner p;
+  let b = Build.of_project p in
+  ignore (Graph.topo b.g);
+  let srcs = List.length (List.concat_map all_srcs p.targets) in
+  Printf.printf "  %s\n"
+    (String.concat (Style.dim ", ")
+       [ Style.plural (List.length p.targets) "target"; Style.plural srcs "source";
+         Style.plural (List.length p.rules) "generated file";
+         Style.plural (Array.length b.g.Graph.nodes) "action" ])
+
+let () =
+  (try
+     let rest = parse_args (List.tl (Array.to_list Sys.argv)) in
+     if not (Unix.isatty Unix.stdout) then Style.enabled := false;
+     if fl.chdir <> "" then Sys.chdir fl.chdir;
+     match rest with
+     | "build" :: names -> ignore (cmd_build names)
+     | "run" :: rest -> cmd_run rest
+     | "test" :: f -> cmd_test f
+     | "install" :: _ -> cmd_install ()
+     | "configure" :: _ ->
+         let p = configure () in
+         banner p;
+         with_config_header p;
+         Printf.printf "  %s\n" (Style.dim "configured")
+     | "check" :: _ -> cmd_check ()
+     | "targets" :: _ -> cmd_targets ()
+     | "graph" :: _ -> cmd_graph ()
+     | "explain" :: rest -> cmd_explain rest
+     | "compdb" :: _ -> cmd_compdb ()
+     | "watch" :: names -> cmd_watch names
+     | "init" :: rest -> cmd_init rest
+     | "clean" :: _ -> cmd_clean ()
+     | "help" :: _ -> print_endline usage
+     | names -> ignore (cmd_build names)
+   with
+  | Diag.Stop ds -> Diag.print ds; exit 1
+  | Sys_error msg -> prerr_endline ("  " ^ Style.red "error" ^ " " ^ msg); exit 1
+  | Unix.Unix_error (e, f, a) ->
+      prerr_endline ("  " ^ Style.red "error" ^ Printf.sprintf " %s: %s %s" f (Unix.error_message e) a);
+      exit 1)