Takes an expression — source — and sets the field defined by as to the result of the source expression.

Can be used to manipulate fields whose names are not statically known, but computed at runtime.

ParameterTypeRequiredDefault ValueDescription
asstringoptional[a] _getField Name of output field.
sourceexpressionrequired   An expression which evaluates the name of the field to read.

[a] Optional parameters use their default value unless explicitly set.

getField() Function Operation

The function can be used to read fields whose exact name might not be known, by getting the value of a dynamically-named field. This happens when the field name is computed from an expression, so the function works by evaluating this expression as input.

It can also be used to manipulate fields whose names contain a space or - like in:

logscale
deltaTime:= now() - getField("time-in-ms")

getField() Examples

Click + next to an example below to get the full details.

Get the Last Element of an Array

Query
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| index := array:length("foo[]")-1
| fieldName := format("foo[%s]", field=[index])
| result := getField(fieldName)
Introduction

Given an event with an array for field foo[x]: 

foo['a','b','c','d']

Looks up the value of the field which is part of an array of elements, using getField() in combination with expressions: first build the string with the field, then perform getField() in that string to get the result.

Step-by-Step

  1. Starting with the source repository events.

  2. logscale
    | index := array:length("foo[]")-1

    Sets the index as the last element of the array (in this case, [6])

  3. logscale
    | fieldName := format("foo[%s]", field=[index])

    Takes the field index and builds the string foo[6] using format()

  4. logscale
    | result := getField(fieldName)

    Provides the value of the field whose name is foo[6]

  5. Event Result set.

Summary and Results

The output is displayed as follows, where the last column shows the value of fieldName column (which is foo[3]) as the result:

@timestamp@rawstring@timestamp.nanosfieldNamefoo[0]foo[1]foo[2]foo[3]indexresult
2024-03-01T08:43:12{"foo": ["a","b","c","d"]}0foo[3]abcd3d

Get the Value of a Field Stored in Another Field

Query
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result := getField("foo")
Introduction

Given an event with the following fields: 

|------------------|
| foo      | bar   |
| bar      | 123   |
| foo      | quux  |
|------------------|

Do a "direct" lookup where the result is set to the value that is stored in that field, by quoting the string — it takes expressions as input (similar to eval() and test() functions):

Step-by-Step

  1. Starting with the source repository events.

  2. logscale
    result := getField("foo")

    The result is set to the value that is stored in field foo

  3. Event Result set.

Summary and Results
barfooresult
123barbar
<no value>quuxquux

In the same event, using the same query that does not quote the string:

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result := getField(foo)

will get the value of the field which name is stored at foo, so 123 is stored as the result:

barfooresult
123bar123
<no value>quux<no value>

(no result is output for foo=quux as quux does not exist).

Take Field Names as Parameters

Query
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| test(getField(?foo)==?bar)
Introduction

Use the function to take a field name as a parameter.

Given an event with the following fields: 

|----------------------|
| hello      | world   |
|----------------------|

Test if a field exists on an event with a specific value where both the field and the value are given as parameters. This query:

Step-by-Step

  1. Starting with the source repository events.

  2. logscale
    | test(getField(?foo)==?bar)

    Tests if the field given by the parameter ?foo (hello) is equal to the value given by the parameter ?bar (world).

  3. Event Result set.

Summary and Results
hello
world