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<h2 class="title"><a id="analysis-pattern-tokenizer"></a>Pattern Tokenizer<a class="edit_me edit_me_private" rel="nofollow" title="Editing on GitHub is available to Elastic" href="https://github.com/elastic/elasticsearch/edit/2.4/docs/reference/analysis/tokenizers/pattern-tokenizer.asciidoc">edit</a></h2>
</div></div></div>
<p>The <code class="literal">pattern</code> tokenizer uses a regular expression to either split text into
terms whenever it matches a word separator, or to capture matching text as
terms.</p>
<p>The default pattern is <code class="literal">\W+</code>, which splits text whenever it encounters
non-word characters.</p>
<div class="warning admon">
<div class="icon"></div>
<div class="admon_content">
<h3>Beware of Pathological Regular Expressions</h3>
<p>The pattern tokenizer uses
<a href="http://docs.oracle.com/javase/8/docs/api/java/util/regex/Pattern.html" class="ulink" target="_top">Java Regular Expressions</a>.</p>
<p>A badly written regular expression could run very slowly or even throw a
StackOverflowError and cause the node it is running on to exit suddenly.</p>
<p>Read more about <a href="http://www.regular-expressions.info/catastrophic.html" class="ulink" target="_top">pathological regular expressions and how to avoid them</a>.</p>
</div>
</div>
<h3><a id="_example_output_2"></a>Example output<a class="edit_me edit_me_private" rel="nofollow" title="Editing on GitHub is available to Elastic" href="https://github.com/elastic/elasticsearch/edit/2.4/docs/reference/analysis/tokenizers/pattern-tokenizer.asciidoc">edit</a></h3>
<div class="pre_wrapper lang-sense">
<pre class="programlisting prettyprint lang-sense">POST _analyze
{
"tokenizer": "pattern",
"text": "The foo_bar_size's default is 5."
}</pre>
</div>
<div class="sense_widget" data-snippet="snippets/171.sense"></div>
<p>The above sentence would produce the following terms:</p>
<div class="pre_wrapper lang-text">
<pre class="programlisting prettyprint lang-text">[ The, foo_bar_size, s, default, is, 5 ]</pre>
</div>
<h3><a id="_configuration_2"></a>Configuration<a class="edit_me edit_me_private" rel="nofollow" title="Editing on GitHub is available to Elastic" href="https://github.com/elastic/elasticsearch/edit/2.4/docs/reference/analysis/tokenizers/pattern-tokenizer.asciidoc">edit</a></h3>
<p>The <code class="literal">pattern</code> tokenizer accepts the following parameters:</p>
<div class="informaltable">
<table border="0" cellpadding="4px">
<colgroup>
<col/>
<col/>
</colgroup>
<tbody valign="top">
<tr>
<td valign="top">
<p>
<code class="literal">pattern</code>
</p>
</td>
<td valign="top">
<p>
A <a href="http://docs.oracle.com/javase/8/docs/api/java/util/regex/Pattern.html" class="ulink" target="_top">Java regular expression</a>, defaults to <code class="literal">\W+</code>.
</p>
</td>
</tr>
<tr>
<td valign="top">
<p>
<code class="literal">flags</code>
</p>
</td>
<td valign="top">
<p>
Java regular expression <a href="http://docs.oracle.com/javase/8/docs/api/java/util/regex/Pattern.html#field.summary" class="ulink" target="_top">flags</a>.
lags should be pipe-separated, eg <code class="literal">"CASE_INSENSITIVE|COMMENTS"</code>.
</p>
</td>
</tr>
<tr>
<td valign="top">
<p>
<code class="literal">group</code>
</p>
</td>
<td valign="top">
<p>
Which capture group to extract as tokens. Defaults to <code class="literal">-1</code> (split).
</p>
</td>
</tr>
</tbody>
</table>
</div>
<h3><a id="_example_configuration_2"></a>Example configuration<a class="edit_me edit_me_private" rel="nofollow" title="Editing on GitHub is available to Elastic" href="https://github.com/elastic/elasticsearch/edit/2.4/docs/reference/analysis/tokenizers/pattern-tokenizer.asciidoc">edit</a></h3>
<p>In this example, we configure the <code class="literal">pattern</code> tokenizer to break text into
tokens when it encounters commas:</p>
<div class="pre_wrapper lang-sense">
<pre class="programlisting prettyprint lang-sense">PUT my_index
{
"settings": {
"analysis": {
"analyzer": {
"my_analyzer": {
"tokenizer": "my_tokenizer"
}
},
"tokenizer": {
"my_tokenizer": {
"type": "pattern",
"pattern": ","
}
}
}
}
}
POST my_index/_analyze
{
"analyzer": "my_analyzer",
"text": "comma,separated,values"
}</pre>
</div>
<div class="sense_widget" data-snippet="snippets/172.sense"></div>
<p>The above example produces the following terms:</p>
<div class="pre_wrapper lang-text">
<pre class="programlisting prettyprint lang-text">[ comma, separated, values ]</pre>
</div>
<p>In the next example, we configure the <code class="literal">pattern</code> tokenizer to capture values
enclosed in double quotes (ignoring embedded escaped quotes <code class="literal">\"</code>). The regex
itself looks like this:</p>
<pre class="literallayout">"((?:\\"|[^"]|\\")*)"</pre>
<p>And reads as follows:</p>
<div class="ulist itemizedlist">
<ul class="itemizedlist">
<li class="listitem">
A literal <code class="literal">"</code>
</li>
<li class="listitem">
<p>Start capturing:</p>
<div class="ulist itemizedlist">
<ul class="itemizedlist">
<li class="listitem">
A literal <code class="literal">\"</code> OR any character except <code class="literal">"</code>
</li>
<li class="listitem">
Repeat until no more characters match
</li>
</ul>
</div>
</li>
<li class="listitem">
A literal closing <code class="literal">"</code>
</li>
</ul>
</div>
<p>When the pattern is specified in JSON, the <code class="literal">"</code> and <code class="literal">\</code> characters need to be
escaped, so the pattern ends up looking like:</p>
<pre class="literallayout">\"((?:\\\\\"|[^\"]|\\\\\")+)\"</pre>
<div class="pre_wrapper lang-sense">
<pre class="programlisting prettyprint lang-sense">PUT my_index
{
"settings": {
"analysis": {
"analyzer": {
"my_analyzer": {
"tokenizer": "my_tokenizer"
}
},
"tokenizer": {
"my_tokenizer": {
"type": "pattern",
"pattern": "\"((?:\\\\\"|[^\"]|\\\\\")+)\"",
"group": 1
}
}
}
}
}
POST my_index/_analyze
{
"analyzer": "my_analyzer",
"text": "\"value\", \"value with embedded \\\" quote\""
}</pre>
</div>
<div class="sense_widget" data-snippet="snippets/173.sense"></div>
<p>The above example produces the following two terms:</p>
<div class="pre_wrapper lang-text">
<pre class="programlisting prettyprint lang-text">[ value, value with embedded \" quote ]</pre>
</div>
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