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fillnull

Description

Replaces null values with a specified value. Null values are field values that are missing in a particular result but present in another result. Use the fillnull command to replace null field values with a string. You can replace the null values in one or more fields. You can specify a string to fill the null field values or use the default, field value which is zero ( 0 ). ​

Syntax

The required syntax is in bold. ​

fillnull
[value=<string>]
[<field-list>]

Required arguments

None. ​

Optional arguments

field-list
Syntax: <field>...
Description: A space-delimited list of one or more fields. If you specify a field list, all of the fields in that list are filled in with the value you specify. If you specify a field that didn't previously exist, the field is created. If you do not specify a field list, the value is applied to all fields.
value
Syntax: value=<string>
Description: Specify a string value to replace null values. If you do not specify a value, the default value is applied to the <field-list>.
Default: 0

Usage

The fillnull command is a distributable streaming command when a field-list is specified. When no field-list is specified, the fillnull command fits into the dataset processing type. See Command types.

Fields in the event set should have at least one non-null value

Due to the unique behavior of the fillnull command, Splunk software isn't able to distinguish between a null field value and a null field that doesn't exist in the Splunk schema. In order for a field to exist in the schema, it must have at least one non-null value in the event set. To ensure downstream processing of fields by the fillnull command, ensure that there is at least one non-null value for the fields in the event set.

For example, consider the following search:

| makeresults | eval test="123123", test2=null() | fillnull value=NULL

The results look something like this:

_time test
2023-06-07 17:49:45 123123

Notice that the test2 field doesn't show up in the results, even though the eval command created it. The reason the test2 field isn't in the results is that there isn't at least one non-null value for the field in the event set.

If a field doesn't have at least one non-null value in the event set, it's considered a nonexistent field, so downstream commands like the fillnull command can't process it. For example, consider the following search:

| makeresults | eval test="123123" | eval test2=null() | table test test2 | fillnull value=NULL

The results look something like this:

test test2
123123

The search results display the test2 field, but not the intended NULL value. This is because the upstream eval command initially set test2 to null, so the field doesn't exist in the schema.

Now consider the following search:

| makeresults | eval test1=split("123,456", ",") | mvexpand test1 | eval test2=if(test1="123", null(), "abc") | fillnull value=NULL

The results look something like this:

_time test1 test2
2023-06-07 18:22:24 123 NULL
2023-06-07 18:22:24 456 abc

This search generates at least one non-null value for each field and shows the expected behavior by setting the null value of the test2 field to the NULL string. Now all the values display as expected because the test2 field has at least one non-null value.

Examples

1. Fill all empty field values with the default value

​Your search has produced the following search results: ​

_time ACCESSORIES ARCADE SHOOTER SIMULATION SPORTS STRATEGY TEE
2021-03-17 5 17 6 3 5 32
2021-03-16 63 39 30 22 127 56
2021-03-15 65 94 38 42 128 60

​ You can fill all of empty field values with the zero by adding the fillnull command to your search. ​

... | fillnull

​ The search results will look like this: ​

_time ACCESSORIES ARCADE SHOOTER SIMULATION SPORTS STRATEGY TEE
2021-03-17 5 17 6 3 5 32 0
2021-03-16 0 63 39 30 22 127 56
2021-03-15 65 94 38 42 0 128 60

2. Fill all empty fields with the string "NULL"

For the current search results, fill all empty field values with the string "NULL".

... | fillnull value=NULL

3. Fill the specified fields with the string "unknown"

​Suppose that your search has produced the following search results: ​

_time host average_kbps instanenous_kbps kbps
2021/02/14 12:00 danube.sample.com 1.865 3.420
2021/02/14 11:53 mekong.buttercupgames.com 0.710 0.164 1.256
2021/02/14 11:47 danube.sample.com 1.325 2.230
2021/02/14 11:42 yangtze.buttercupgames.com 2.249 0.000 2.249
2021/02/14 11:39 2.874 3.841 1.906
2021/02/14 11:33 nile.example.net 2.023 0.915

​ You can fill all empty field values in the "host" and "kbps" fields with the string "unknown" by adding the fillnull command to your search. ​

... | fillnull value=unknown host kbps

​ ​The results look like this:

_time host average_kbps instanenous_kbps kbps
2021/02/14 12:00 danube.sample.com 1.865 3.420
2021/02/14 11:53 mekong.buttercupgames.com 0.710 0.164 1.256
2021/02/14 11:47 danube.sample.com 1.325 2.230
2021/02/14 11:42 yangtze.buttercupgames.com 2.249 0.000 2.249
2021/02/14 11:39 unknown 2.874 3.841 1.906
2021/02/14 11:33 nile.example.net 2.023 0.915 unknown

​ ​If you specify a field that does not exist the field is created and the value you specify is added to the new field. ​ For example if you specify bytes in the field list, the bytes field is created and filled with the string "unknown". ​

... | fillnull value=unknown host kbps bytes

​ ​The results look like this:

_time host average_kbps instanenous_kbps kbps bytes
2021/02/14 12:00 danube.sample.com 1.865 3.420 unknown
2021/02/14 11:53 mekong.buttercupgames.com 0.710 0.164 1.256 unknown
2021/02/14 11:47 danube.sample.com 1.325 2.230 unknown
2021/02/14 11:42 yangtze.buttercupgames.com 2.249 0.000 2.249 unknown
2021/02/14 11:39 unknown 2.874 3.841 1.906 unknown
2021/02/14 11:33 nile.example.net 2.023 0.915 unknown unknown

4. Use the fillnull command with the timechart command

Build a time series chart of web events by host and fill all empty fields with the string "NULL".

sourcetype="web" | timechart count by host | fillnull value=NULL

See also

Related commands
filldown
streamstats
Last modified on 13 June, 2023
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This documentation applies to the following versions of Splunk Cloud Platform: 9.1.2312, 9.0.2208, 8.2.2201, 8.2.2202, 8.2.2203, 9.0.2205, 8.2.2112, 9.0.2209, 9.0.2303, 9.0.2305 (latest FedRAMP release), 9.1.2308


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