Add check_for_file and check_for_tool functions to common.sh

common.sh

Index: common.sh
diff --git a/common.sh b/common.sh
index 1d25074316d2a336046e3a5311cc1d6de5b02a37..ac10de6e1c5df104232427793c304eab80a57ec0 100644
--- a/common.sh
+++ b/common.sh
@@ -647,3 +647,36 @@ prepare_test_image() {
   # From now on we use the just-created test image
   CHROMEOS_RETURN_VAL="$1/${CHROMEOS_TEST_IMAGE_NAME}"
 }
+
+# Check that the specified file exists.  If the file path is empty or the file
+# doesn't exist on the filesystem generate useful error messages.  Otherwise
+# show the user the name and path of the file that will be used.
+check_for_file() {
+  local name=$1
+  local padding=$2
+  local path=$3
+
+  if [ -z "${path}" ]; then
+    error "No ${name} file specified." && exit

[davidjames, 2011/03/01 00:09:49]

1. Looks like this is exiting with a success code. Shouldn't it exit with an
error code? Same comment below.
2. Should we just use 'die' instead if you want to exit?

[robotboy, 2011/03/01 00:20:19]

Done.

+  fi
+
+  if [ ! -e "${path}" ]; then
+    error "No ${name} file found at: ${path}" && exit
+  else
+    info "Using ${name}${padding}: ${path}"
+  fi
+}
+
+# Check that the specified tool exists.  If it does not exist in the PATH
+# generate a useful error message indicating how to install the ebuild
+# that contains the required tool.
+check_for_tool() {
+  local tool=$1
+  local ebuild=$2
+
+  if ! which "${tool}" >/dev/null ; then
+    error "The ${tool} utility was not found in your path.  Run the following"
+    error "command in your chroot to install it: sudo -E emerge ${ebuild}"
+    exit
+  fi
+}