First pass at "pub update" implementation.

utils/pub/command_update.dart

Index: utils/pub/command_update.dart
diff --git a/utils/pub/command_update.dart b/utils/pub/command_update.dart
index c1fe4f4816b65723c926c8684b30c3770c32da77..2bc03f76ec313fdab3fdb846b852b2490ae56d8e 100644
--- a/utils/pub/command_update.dart
+++ b/utils/pub/command_update.dart
@@ -4,5 +4,24 @@
 
 /** Handles the `update` pub command. */
 void commandUpdate(PubOptions options, List<String> args) {
-  throw 'not implemented yet';
+  // TODO(rnystrom): Should validate args.
+
+  var entrypoint;
+  var packagesDir;
+  var dependencies;

[nweiz, 2012/04/25 17:50:47]

These should be listed in the same order they're assigned.

[Bob Nystrom, 2012/04/25 22:20:29]

Done.

+
+  getWorkingPackage().chain((package) {
+    entrypoint = package;
+    return package.traverseDependencies();
+  }).chain((packages) {
+    dependencies = packages;
+    // TODO(rnystrom): Make this path configurable.
+    packagesDir = join(entrypoint.dir, 'packages');
+    return cleanDir(packagesDir);
+  }).then((dir) {
+    // Symlink each dependency.
+    for (final package in dependencies) {
+      createSymlink(package.dir, join(packagesDir, package.name));
+    }
+  });
 }