First stab at "pub run" command.

sdk/lib/_internal/pub/lib/src/command/run.dart

Index: sdk/lib/_internal/pub/lib/src/command/run.dart
diff --git a/sdk/lib/_internal/pub/lib/src/command/run.dart b/sdk/lib/_internal/pub/lib/src/command/run.dart
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+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+library pub.command.run;
+
+import 'dart:async';
+import 'dart:io';
+
+import 'package:barback/barback.dart';
+import 'package:stack_trace/stack_trace.dart';
+
+import '../barback/asset_environment.dart';
+import '../command.dart';
+import '../exit_codes.dart' as exit_codes;
+import '../io.dart';
+import '../log.dart' as log;
+import '../utils.dart';
+
+final _arrow = getSpecial('\u2192', '=>');
+
+/// Handles the `run` pub command.
+class RunCommand extends PubCommand {
+  bool get takesArguments => true;
+  bool get allowTrailingOptions => false;
+  String get description => "Run an executable from a package.";
+  String get usage => "pub run <executable> [args...]";
+
+  Future onRun() {
+    if (commandOptions.rest.isEmpty) {
+      usageError("Must specify an executable to run.");
+    }
+
+    // Unless the user overrides the verbosity, we want to filter out the
+    // normal pub output shown while loading the environment.
+    if (log.verbosity == log.Verbosity.NORMAL) {
+      log.verbosity = log.Verbosity.WARNING;
+    }
+
+    var environment;
+    return AssetEnvironment.create(entrypoint, BarbackMode.RELEASE,
+        WatcherType.NONE, useDart2JS: false)
+          .then((_environment) {
+      environment = _environment;
+
+      // Show in-progress errors, but not results. Those get handled
+      // implicitly by getAllAssets().
+      environment.barback.errors.listen((error) {
+        log.error(log.red("Build error:\n$error"));
+      });
+
+      return environment.serveDirectory("bin");
+    }).then((server) {
+      var script = commandOptions.rest[0];
+      var args = commandOptions.rest.skip(1).toList();
+
+      // TODO(rnystrom): Support scripts in other directories.
+      var scriptPath = "bin/$script.dart";
+
+      // Try to make sure the entrypoint script exists (or is generated) before
+      // we spawn the process to run it.
+      return environment.barback.getAssetById(
+          new AssetId(entrypoint.root.name, scriptPath)).then((_) {
+        return environment.getUrlsForAssetPath(scriptPath).then((urls) {
+          // Should only be bound to one port.
+          assert(urls.length == 1);
+
+          // Run in checked mode.
+          // TODO(rnystrom): Make this configurable.
+          args.insert(0, "--checked");
+
+          // The URL to the Dart entrypoint comes before the script arguments.
+          args.insert(1, urls[0].toString());
+          return Process.start(Platform.executable, args);
+        }).then((process) {
+          // Note: we're not using process.std___.pipe(std___) here because
+          // that prevents pub from also writing to the output streams.
+          process.stderr.listen(stderr.add);
+          process.stdout.listen(stdout.add);
+          stdin.listen(process.stdin.add);
+
+          return process.exitCode;
+        }).then(flushThenExit);
+      }).catchError((error, stackTrace) {
+        if (error is! AssetNotFoundException) throw error;
+
+        log.error("Could not find $scriptPath.");
+        log.fine(new Chain.forTrace(stackTrace));
+        return flushThenExit(exit_codes.NO_INPUT);
+      });
+    });
+  }
+}