Splunk Search

extract from calculated field

Splunk Employee
Splunk Employee

I can't find anything that says you can't do a field extraction from a calculated field, but I found that this works in props.conf:

[psft_weblogic_access]
EVAL-url = urldecode(url_encoded)
EXTRACT-url_encoded = (GET|POST)\s(?P.?)\s
EXTRACT-url_path = (?P.
?)(\?|$) in url_encoded

but this does not work--url_path is not extracted:

[psft_weblogic_access]
EVAL-url = urldecode(url_encoded)
EXTRACT-url_encoded = (GET|POST)\s(?P.?)\s
EXTRACT-url_path = (?P.
?)(\?|$) in url

Is that a limitation?

(url_path is meant to grab everything up to the first "?" or to the end of the url.)

Tags (1)
0 Karma
1 Solution

Splunk Employee
Splunk Employee

Calculated fields happen after field aliasing (which happens after ALL field extractions) but before lookups. What you're observing here is the correct behavior and not a limitation. eval is flexible enough to allow you to wrangle and mold field/strings to the desired shape. Your first example "works" because you're not extracting anything from url after it is calculated. Your second example, as expected, does not work because you're trying to extract from an EVALed field.

Also, note that you can't EVAL an EVALed field, but nothing prevents you from making your eval statement as complex as necessary:

[psft_weblogic_access]
EVAL-url_path = replace(urldecode(url_encoded), "([^?]+).*$", "\1")

d.

View solution in original post

Splunk Employee
Splunk Employee

Calculated fields happen after field aliasing (which happens after ALL field extractions) but before lookups. What you're observing here is the correct behavior and not a limitation. eval is flexible enough to allow you to wrangle and mold field/strings to the desired shape. Your first example "works" because you're not extracting anything from url after it is calculated. Your second example, as expected, does not work because you're trying to extract from an EVALed field.

Also, note that you can't EVAL an EVALed field, but nothing prevents you from making your eval statement as complex as necessary:

[psft_weblogic_access]
EVAL-url_path = replace(urldecode(url_encoded), "([^?]+).*$", "\1")

d.

View solution in original post

Splunk Employee
Splunk Employee

It is likely that EXTRACTs all run before EVALs, so you would not be able to extract this way. However, you may be able to instead use REPORT/transforms.conf to extract from EVAL. REPORTs run after EXTRACTs, but I do not know if they run after EVALs. If they do, you should be able to use:

REPORT-url_path = url_path

and in transforms.conf:

[url_path]
SOURCE_KEY = url
REGEX = (?<url_path>.?)(?|$)

in place of the corresponding EXTRACT.

0 Karma