Skip to content
SPL // Splunk

Using the regex Command

KGI Avatar

Written by: Ellis DeVaney | Last Updated:

March 29, 2024
using the regex command in splunk

Originally Published:

April 3, 2024

Splunk, a powerful data analytics platform, enables users to collect, index, and analyze machine data from various sources. The Search Processing Language (SPL) lies at Splunk’s heart, allowing users to search, filter, and manipulate data easily. Moreover, the regex command, which stands for regular expression, is an essential command in SPL. A regular expression is a sequence of characters that defines a search pattern. As any Splunker will tell you, regular expressions play a crucial role in searching for data in Splunk. In this blog, we will review the regex command in more detail.

When to Utilize the regex Command

The regex command in Splunk is designed for searching events using regular expressions. Regular expressions are powerful patterns that match and manipulate text based on specific rules. Users can utilize the regex command to define patterns and extract information from log files, network traffic data, and other sources. When searching data in Splunk, you will inevitably need to use a regular expression to get the outcome you need. Regular expressions, just like in any programming language, are critical to searching and data manipulation.

Proper Command Syntax

The basic syntax for the regex command in Splunk is as follows:

					... | regex <field>=<regular_expression> 
  • field: Specifies the field in the event data to search, similar to common | search <field>=<value> syntax.

  • regular_expression: The regular expression pattern to match against the values of field.

Sample Use Cases

Example 1: Using the regex command to extract IP Addresses from Log Files

Use Case: Search data for a specific pattern, looking for internal IP addresses in web access logs.

Description: In this example, we’ll use the regex command to extract IP addresses from an event in Splunk.

					sourcetype=access_logs | regex host_ip="10\.\d{1,3}\.\d{1,3}\.\d{1,3}"

In this example, the search initially filters events based on the “sourcetype” field, including only events from the “access_logs” sourcetype. Then, the regex command searches the host_ip field for IP addresses using the regular expression pattern. The IPs returned match values of the 10.x.x.x IP range. This logic can be applied to specific subnets of interest using combinations of octet values and regex pattern matches.

Example 2: Identify Poor Field Extractions

Use Case: Search data for field values that have leading whitespace included in the extracted string.

Description: In this example, we’ll use the regex command to extract a hostname.

					sourcetype=access_logs | regex hostname="^\s+\w+"

The search has extracted a field called hostname. However, they’ve discovered some hostname values have a leading whitespace. This has led to inaccurate statistical reports. By searching the hostname field using the regex command, they are able to filter out the hostnames with leading whitespaces.

An alternative version of the same search demonstrates the use of the != (not equal to) operator. Using != with regex in this example, will search for hostname values that do not begin with word characters.

					sourcetype=access_logs | regex hostname!="^\w+"

Comparing Regular Expression Commands in Splunk

The Splunk regex command, along with rex and erex, share the purpose of utilizing regular expressions to search, filter, or transform event data. The regex command is primarily used for filtering search results based on a regular expression pattern. It discards events that do not match the provided pattern.

Similarly, rex is employed to extract fields from your data at search time, allowing for more complex data manipulation and enrichment by using named capturing groups in regular expressions. 

In contrast, erex, simplifies the field extraction process by allowing users to provide examples of the data from which they want to extract fields, and then Splunk generates the regular expressions automatically. 

Despite their different applications—regex for filtering, rex for field extraction, and erex for generating regex patterns based on examples—all three commands leverage the power of regular expressions, making them integral tools in Splunk for data parsing and analysis.


The regex command empowers users to search data effectively using regular expressions, offering a robust solution for complex pattern matching and data extraction in Splunk. By mastering this command, users can enhance their data analysis capabilities. Here are three key takeaways to help you master this command:

  • Precision in Data Search: The regex command empowers users to conduct searches by leveraging regular expressions, enabling them to locate patterns or values within their data.
  • Syntax and Usage: Effective data validation and analysis in Splunk hinge on understanding the proper syntax and usage of the regex command.
  • Combining Commands: Combining the regex command with other Splunk commands and functions can enhance your ability to parse, transform, and manipulate data. Further unlocking deeper insights and enabling more comprehensive analysis.

To get access to more Splunk searches like the ones in this article, check out the Atlas Search Library which is one of the elements in the Atlas Platform. Atlas Search Library is a curated list of optimized searches that you can use to empower your Splunk users to search without having to learn SPL. You can also create, customize and maintain your own library of searches to ensure that your users are getting the most from using Splunk in your environment.

Helpful? Don't forget to share this post!