Not a valid regular expression file – How to solve this Elasticsearch exception

Opster Team

August-23, Version: 6.8-8.9

Briefly, this error occurs when Elasticsearch tries to interpret a file as a regular expression, but the file’s content doesn’t match the regular expression syntax. This could be due to incorrect formatting or special characters that aren’t properly escaped. To resolve this issue, you can 1) Review the file content and ensure it follows the correct regular expression syntax. 2) Escape any special characters that might be causing the error. 3) If the file isn’t meant to be a regular expression, check your Elasticsearch configuration to ensure it’s not being incorrectly interpreted as such.

This guide will help you check for common problems that cause the log ” not a valid regular expression file ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: .

Log Context

Log “not a valid regular expression file” class name is We extracted the following from Elasticsearch source code for those seeking an in-depth context :

 }  if (patternListKeys.size() != deviceTypePatterns.size()) {
 throw new ElasticsearchParseException("not a valid regular expression file");
 }  public String findDeviceType(String agentString; VersionedName userAgent; VersionedName os; VersionedName device) {
 if (deviceTypePatterns.isEmpty()) {


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