support multi-level symlinks to SDK exes

sdk/bin/pub

 #!/bin/bash
 # Copyright (c) 2012, 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.
 
 # Run pub.dart on the Dart VM. This script assumes the Dart SDK's directory
 # structure.
 
-function follow_links() {
-  file="$1"
-  while [ -h "$file" ]; do
-    # On Mac OS, readlink -f doesn't work.
-    file="$(readlink "$file")"
-  done
-  echo "$file"
-}
+PROG_NAME=$(cd -P -- "$(dirname -- "$0")" && pwd -P) && \
+  PROG_NAME=$PROG_NAME/$(basename -- "$0")
 
-# Unlike $0, $BASH_SOURCE points to the absolute path of this file.
-PROG_NAME="$(follow_links "$BASH_SOURCE")"
+# resolve symlinks
+while [ -h $PROG_NAME ]; do
+    DIR=$(dirname -- "$PROG_NAME")
+    SYM=$(readlink $PROG_NAME)
+    PROG_NAME=$(cd $DIR && cd $(dirname -- "$SYM") && pwd)/$(basename -- "$SYM")
+done
 
 # Handle the case where dart-sdk/bin has been symlinked to.
 BIN_DIR="$(cd "${PROG_NAME%/*}" ; pwd -P)"
 
 SDK_DIR="$(cd "${BIN_DIR}/.." ; pwd -P)"
 
 SNAPSHOT="$BIN_DIR/snapshots/pub.dart.snapshot"
 
 if test -f "$SNAPSHOT"; then
   # We are running the snapshot in the built SDK.
@@ skipping 15 matching lines @@
 
   # Use the Dart binary in the built SDK so pub can find the version file next
   # to it.
   DART="$BUILD_DIR/dart-sdk/bin/dart"
   PACKAGES_DIR="$BUILD_DIR/packages/"
 
   PUB="$SDK_DIR/lib/_internal/pub/bin/pub.dart"
 
   exec "$DART" "--package-root=$PACKAGES_DIR" "$PUB" "$@"
 fi