How can I search for a missing field?

[hulahoop]

Let's say I have events A and B:

A -- Feb 1 2010 10:10:00 field1=foo field2=bar
B -- Feb 1 2010 10:10:01 field1=foo

How can I find all events where field2 is missing (essentially event B in this tiny example)?

[support0]

fillnull field2 | search field2=0

[dinh]

You can do this on your search:

| where isnull(field2)

[lmoceze]

Thats the answer, thanks!

[gkanapathy]

Note that using

field2!=*

will not work either. This will never return any events, as it will always be false. This means that field2!=* and NOT field2=* are not entirely equivalent. In particular, in the case where field2 doesn't exist, the former is false, while the latter is true.

[gkanapathy]

Well, I guess it depends what you mean by "logically equivalent", but there is a difference in meaning regardless of how Splunk treats them.

[gkanapathy]

No they are not logically equivalent. There is a difference between being empty, and not existing.

[hulahoop]

It seems like they are logically equivalent, but Splunk does not treat them so. Is that a fair statement?

[hulahoop · Accepted solution]

Ok, so I tried a few things, and this is what ended up working:

NOT field2=*

It would be more intuitive if this worked also:

field2=""

[leonjxtan]

the first code works; the second code doesn't.

[otman01]

it works thank you all , have a nice day

[gkanapathy]

Yes, it can happen.

[hulahoop]

hey k8to, i'm just wondering if it can actually happen, and if splunk would behave consistently.

[jrodman]

It's a valid state of a field.
You can get there with regex extractions.

Do you mean that this is an undesirable thing?

[hulahoop]

yes, but in splunk land, would a field ever exist and be empty?

[gkanapathy]

field2="" means something very different. It means that field2 exists, but has an empty string value.