Eval

This topic describes how to use the function in the .

Description

The Eval function calculates an expression and puts the resulting value into the record as a new field.

• If the field name that you specify does not match a field in the data stream, a new top-level field is added to your record.
• If the field name that you specify matches a field name that already exists in the data stream, the results of the eval expression overwrite the values in that field.

You can chain multiple eval expressions in a single Eval function using a comma to separate subsequent expressions. The Eval function processes multiple eval expressions in-order and lets you reference previously evaluated fields in subsequent expressions.

How the Eval function works

Most of the time the Eval function is used to create a new top-level field in your data and the values in that new field are the result of an expression. There are many types of expressions you can specify.

Using Eval functions

There are dozens of scalar functions that you can use in the eval expression. The functions are organized into these categories:

• Casting functions
• Conditional functions
• Conversion functions
• Cryptographic functions
• Date and Time functions
• Iterator functions
• List functions
• Map functions
• Mathematical functions
• String manipulation

For examples of how to use these scalar functions in your Eval function, see the Examples on this page.

Difference between Select and Eval

Both functions are used to change the fields in the record. However, while the Eval function keeps existing fields and adds new fields for the aliases in the eval, The Select function only includes the fields explicitly specified in the select function.

Syntax

The required syntax is in bold.

eval

<field>=<expression> ["," <field>=<expression> ]...

Function Input/Output Schema

Function Input

collection<record<R>>

This function takes in collections of records with schema R.

Function Output

collection<record<S>>

This function outputs the same collection of records but with a different schema S.

Required arguments

field

Syntax: <string>

Description: A destination field name for the resulting calculated value. If the field name already exists in your events, eval overwrites the value.

expression

Syntax: <string>

Description: A combination of values, variables, operators, and functions that will be executed to determine the value to place in your destination field.

Examples

Examples of common use cases follow. These examples assume that you have added the function to your pipeline.

1. SPL2 Example: Change the value of source_type field

This example assumes that you are in the SPL View.

...| eval source_type="ASA" |...;

2. SPL2 Example: Replace a string and return the replacement string in a new field

This example assumes that you are in the SPL View.

In this example, the replace function is used to perform a text replacement. Returns "foobar" in a new top-level field called newfield.

... | eval newfield=replace("bar", /(bar)/, "foo$1");

3. SPL2 Example: Use the if function to analyze field values

This example assumes that you are in the SPL View.

Create a new field called error in each record. Using the if function, set the value in the error field to OK if the status value is 200. Otherwise set the error field value to Problem.

...| eval error = if(status == 200, "OK", "Problem") |...;

Extract metrics data from body field

...| eval metrics=extract_regex(cast(body, "string"), /group=(?<group>S+),s?series="(?<series>[^"]+)",s?(?<data>.*)$/) |...;

4. SPL2 Example: Add the key-value pair "some_key": "some_value" to the map in the attributes field

This example assumes that you are in the SPL View.

...| eval attributes=map_set(attributes, "some_key", "some_value")| ...;