Not a valid regular expression file – Elasticsearch Error How To Solve Related Issues

Not a valid regular expression file – Elasticsearch Error How To Solve Related Issues

Updated: July-20

Elasticsearch Version: 1.7-8.0

Before you begin reading this guide, we recommend you try running the Elasticsearch Error Check-Up  which can resolve issues causing many errors 


This guide will help you check for common problems that cause the log “not a valid regular expression file” to appear. It’s important to understand the issues related to the log, so to get started, read the general overview on common issues and tips related to the Elasticsearch concepts: .

Advanced users might want to skip right to the common problems section in each concept or try running the Check-Up which analyses ES to discover the cause of many errors and provides suitable actionable recommendations (free tool that requires no installation). 

Log Context

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

  if (uaPatterns.isEmpty() && osPatterns.isEmpty() && devicePatterns.isEmpty()) {
  throw new ElasticsearchParseException("not a valid regular expression file");
  private Pattern compilePattern(String regex; String regex_flag) {
  // Only flag present in the current default regexes.yaml

Related issues to this log

We have gathered selected Q&A from the community and issues from Github, that can help fix related issues please review the following for further information :

1 Regular expression to match DNS hostname or IP Address? -views 341,274 ,score 372

Is there a regular expression to detect a valid regular expression? -views   210,041,score 1017

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