elasticsearch/docs/reference/text-analysis/character-filter-reference.md

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Character filter reference [analysis-charfilters]

Character filters are used to preprocess the stream of characters before it is passed to the tokenizer.

A character filter receives the original text as a stream of characters and can transform the stream by adding, removing, or changing characters. For instance, a character filter could be used to convert Hindu-Arabic numerals (٠‎١٢٣٤٥٦٧٨‎٩‎) into their Arabic-Latin equivalents (0123456789), or to strip HTML elements like <b> from the stream.

Elasticsearch has a number of built in character filters which can be used to build custom analyzers.

HTML Strip Character Filter : The html_strip character filter strips out HTML elements like <b> and decodes HTML entities like &.

Mapping Character Filter : The mapping character filter replaces any occurrences of the specified strings with the specified replacements.

Pattern Replace Character Filter : The pattern_replace character filter replaces any characters matching a regular expression with the specified replacement.