Issue 6577: remove confirmation to delete output directory

build_image

Index: build_image
diff --git a/build_image b/build_image
index b4a6f1ac62add3154243086d7f6349c9acbafc23..6e2aa0e8a8c1a79f3c779fe63223a2765870af93 100755
--- a/build_image
+++ b/build_image
@@ -319,14 +319,21 @@ cleanup() {
 delete_prompt() {
   echo "An error occurred in your build so your latest output directory" \
     "is invalid."
-  read -p "Would you like to delete the output directory (y/N)? " SURE
-  SURE="${SURE:0:1}" # Get just the first character.
+
+  # Only prompt if both stdin and stdout are a tty. If either is not a tty,
+  # then the user may not be present, so we shouldn't bother prompting.
+  if tty -s && tty -s <&1; then
+    read -p "Would you like to delete the output directory (y/N)? " SURE
+    SURE="${SURE:0:1}" # Get just the first character.
+  else
+    SURE="y"
+    echo "Running in non-interactive mode so deleting output directory."
+  fi
   if [ "${SURE}" == "y" ] ; then
     sudo rm -rf "${OUTPUT_DIR}"
     echo "Deleted ${OUTPUT_DIR}"
   else
-    echo "Not deleting ${OUTPUT_DIR}. Note dev server updates will not work" \
-      "until you successfully build another image or delete this directory"
+    echo "Not deleting ${OUTPUT_DIR}."
   fi
 }