The pattern_capture token filter, unlike the pattern tokenizer, emits a token for every capture group in the regular expression. Patterns are not anchored to the beginning and end of the string, so each pattern can match multiple times, and matches are allowed to overlap.

For instance a pattern like :

"(([a-z]+)(\d*))"

when matched against:

"abc123def456"

would produce the tokens: [ abc123, abc, 123, def456, def, 456 ]

If preserve_original is set to true (the default) then it would also emit the original token: abc123def456.

This is particularly useful for indexing text like camel-case code, eg stripHTML where a user may search for "strip html" or "striphtml":

PUT test
{
   "settings" : {
      "analysis" : {
         "filter" : {
            "code" : {
               "type" : "pattern_capture",
               "preserve_original" : true,
               "patterns" : [
                  "(\\p{Ll}+|\\p{Lu}\\p{Ll}+|\\p{Lu}+)",
                  "(\\d+)"
               ]
            }
         },
         "analyzer" : {
            "code" : {
               "tokenizer" : "pattern",
               "filter" : [ "code", "lowercase" ]
            }
         }
      }
   }
}

When used to analyze the text

import static org.apache.commons.lang.StringEscapeUtils.escapeHtml

this emits the tokens: [ import, static, org, apache, commons, lang, stringescapeutils, string, escape, utils, escapehtml, escape, html ]

Another example is analyzing email addresses:

PUT test
{
   "settings" : {
      "analysis" : {
         "filter" : {
            "email" : {
               "type" : "pattern_capture",
               "preserve_original" : true,
               "patterns" : [
                  "([^@]+)",
                  "(\\p{L}+)",
                  "(\\d+)",
                  "@(.+)"
               ]
            }
         },
         "analyzer" : {
            "email" : {
               "tokenizer" : "uax_url_email",
               "filter" : [ "email", "lowercase",  "unique" ]
            }
         }
      }
   }
}

When the above analyzer is used on an email address like:

john-smith_123@foo-bar.com

it would produce the following tokens:

john-smith_123@foo-bar.com, john-smith_123,
john, smith, 123, foo-bar.com, foo, bar, com

Multiple patterns are required to allow overlapping captures, but also means that patterns are less dense and easier to understand.

Note: All tokens are emitted in the same position, and with the same character offsets. This means, for example, that a match query for john-smith_123@foo-bar.com that uses this analyzer will return documents containing any of these tokens, even when using the and operator. Also, when combined with highlighting, the whole original token will be highlighted, not just the matching subset. For instance, querying the above email address for "smith" would highlight:

  <em>john-smith_123@foo-bar.com</em>

not:

  john-<em>smith</em>_123@foo-bar.com