ES example of groovy not throwing any exceptions when ctx._source is misspelled.

es_groovy_issue.sh

export ES_HOST=http://localhost:9200

# Create an index we will call it users
curl -XPUT $ES_HOST/users

# Configure mapping, files with path and size
curl -XPUT $ES_HOST/users/files/_mapping -d '
{
  "doc": {
      "properties": {
        "path": {"type": "string"},
        "size": {"type": "long"}
      }
  }
}'

# index some files/documents
curl -X PUT $ES_HOST/users/files/1 -d '
{
   "path" : "usr/files/somefile.txt",
   "size" : 500
}'

curl -X PUT $ES_HOST/users/files/2 -d '
{
   "path" : "usr/files/somefile2.txt",
   "size" : 700
}'

# Now using the search by query plugin, try renaming the file with a script
curl -XPOST  $ES_HOST/users/files/_update_by_query -d ' 
{
  "query": {
    "bool": {
      "must": [
        {
          "term": {
            "path": "usr/files"
          }
        }]
    }
  },
  "script": "def str = ctx_source.path;\ndef str2 = str.replaceAll(\"usr/files\", \"usr/files2\");\nctx._source.path = str2;"
}'

# The result will look like this
# {
#   "ok":true,
#   "took":14,
#   "total":2,
#   "updated":0,
#   "indices":[
#     {
#       "new_index":{}
#     }]
# }

# As it indicate that the query was able to match the two docs yet they did not get updated
# Nothing in the log indicates as to why it failed to update
# If you have a sharp eye you will notice that in the _update_by_query script we are missing a '.'
# def str = ctx_source should be ctx._source
# yet groovy never complains about ctx_source not being in scope

# Updating the script will get the job done
curl -XPOST  $ES_HOST/users/files/_update_by_query -d ' 
{
  "query": {
    "bool": {
      "must": [
        {
          "term": {
            "path": "usr/files"
          }
        }]
    }
  },
  "script": "def str = ctx._source.path;\ndef str2 = str.replaceAll(\"usr/files\", \"usr/files2\");\nctx._source.path = str2;"
}'

# And now all documents have been updates successfully
# {
#   "ok":true,
#   "took":12,
#   "total":2,
#   "updated":2,
#   "indices":[
#     {
#       "new_index":{}
#     }]
# }