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KQL query for removing the pipe symbol ("|") from strings.

In this blog post, we will explore how to remove the trailing pipe symbol ("|") from strings using Kusto Query Language (KQL). We'll focus on a syslog-based parser scenario where important fields like hostname and username have the pipe symbol as the last character.

When working with syslog data, it's common to encounter strings with a trailing pipe symbol. For instance, the machine name may appear as "machine01|" and the username as "user01|". To process and analyze this data accurately, it's crucial to remove the trailing pipe symbol from these strings.

The Initial Attempt: As we embarked on our quest to remove the trailing pipe symbol from strings, our first attempt involved using the trim_end function. Our initial query looked like this:

Syslog | extend HostName01 = extract(".*dstHost=(.*?)dst.*", 1, SyslogMessage) | extend HostName = trim_end("|", HostName01)

| project HostName, HostName01

Unfortunately, our initial efforts didn't yield the desired outcome. The resulting table showed that the pipe symbol was still present at the end of the strings:





Not to be discouraged, we delved deeper into the vast array of KQL functions and operators to find an alternative solution. Our objective was clear: remove the trailing pipe symbol from the strings.

After exploring various functions and brainstorming potential solutions, we stumbled upon the "replace_string" operator. This operator allows us to replace specific characters or substrings within a string.

Example Query:

Let's consider an example where we have a syslog dataset and want to extract the destination hostname while removing the trailing pipe symbol. Here's a sample query:

Syslog | extend HostName01 = extract(".*dstHost=(.*?)dst.*", 1, SyslogMessage) | extend HostName = replace_string(HostName01, "|", "") | project HostName, HostName01


  1. The extend operator is used to create a new column HostName01 by extracting the desired value using a regular expression.

  2. Next, we use the extend operator again to create a new column HostName, where we replace the trailing pipe symbol with an empty string using the replace_string function.

  3. Finally, we use the project operator to select and display only the desired columns (HostName and HostName01).


By leveraging the power of KQL and the replace_string operator, we can easily remove trailing pipe symbols from strings in our syslog-based parser. This ensures accurate processing and analysis of important fields like hostname and username. The example query provided demonstrates the step-by-step approach to extract and modify the string, ultimately resulting in the desired output.

KQL provides a flexible and efficient way to manipulate and transform data, allowing us to tackle various parsing and data processing challenges effectively. With this newfound knowledge, we can enhance your syslog parsing workflows and unlock valuable insights from your data.

Remember to adjust the column names and capitalization based on your specific scenario, as KQL is case-sensitive. Happy parsing!

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