domanchi/cheatsheet.md

## cheatsheet.md

      
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    Splunk Queries

I really don't like Splunk documentation. Why is it so hard to find out how to do a certain action? So this is a cheatsheet that I constructed to help me quickly gain knowledge that I need.
Analysis

Events over time

index="my_log"
| bin span=1hr _time
| stats count by _time

OR
index="my_log"
| timechart count span=1hr

Arrays

Does an array contain a specific value?

"array_name{}"=value

# Nested arrays
"dictionary_name.array_name{}.dictionary2.deep_nested_array{}"=value

Extracting values from an array

eval variable_name=mvindex('array_name{}', array_index)

Strings

String Matching (with whitespace supression)

If you're unable to match field values as you expect, extract the non-whitespace values from the field and compare against that instead.
For example, in the below example, context.messageStatus may contain whitespace, so Splunk won't capture them with a standard =. Instead, we need to do the following:
index="my_log"
| rex field=context.MessageStatus "(?<messageStatus>\w+)"
| eval status=if(messageStatus = "undelivered", "fail", "success")
| search status="success"

If you're trying to get multiple matches, use max_match, where max_match=0 finds unlimited matches.
String Replacement

rex mode=sed field=your_field "regex_statement"

# This is especially handy when you want to ignore whitespace!
# Example:
#    rex mode=sed field=my_field "s/ //g"

String Concatenation

eval variable_name = "string1" . "string2"

# This is just like PHP
# Example:
#     eval word = "foo" . "bar" | table word
#
# Output:
#    word
#    ----
#    foobar 

Substrings

eval variable_name = substr(variable, start_index, length)

# Example:
#    eval word = "foobar" | eval short = substr(word, 1, 3) | table short
#
# Output:
#    short
#    -----
#    oob

eval

Trying to use a nested value in a dictionary, in an eval statement? Use rename first!
Example Entry:
{
    "signals": {
        "ip_address": "1.2.3.4",
    },
}

Query:
    | rename signals.ip_address as ip_addr
    | eval ip_addr=if(isnull(ip_addr), "null", ip_addr)

Working with Multiple Queries

Subsearch

This is used for funneling the output of one splunk query, into another query. However, some older splunk versions do not support it. However, there are other ways to formulate your query! See this link for inspiration.
Example Logs:

nginx_logs
----------
{
	"useragent": "Chrome",
	"status":    200,
	"user":      "random-hash",
}

api_logs
--------
{
	"endpoint":   "/userinfo",
	"request-id": "random-hash",
}

Objective: Find out the useragent

Query:
    index=*
        (endpoint="/userinfo" AND request-id="random-hash") OR user="random-hash"
        | stats count by useragent
 
Explanation:
This searches all logs and tries to cross-reference a request-id from `api_logs`, and
searches for its useragent from `nginx_logs`. Note that the search parameters for the
log in `api_logs` should be as unique as possible, so that it won't pull information
from other logs.

Joins

Joins are handy, when they work. This is a semi-complicated example I've used:
Example Logs:

suspicious_ips
--------------
{
    "ip_address": "1.2.3.4",
}

valid_ips
-----------
{
    "ip_address": "1.2.3.4",
}

Objective: Determine which IPs in `suspicious_ips` have NOT been logged in `valid_ips`.

Query:
    sourcetype=suspicious_ips
        | join type=left ip_address [
            search search_name=valid_ips
            | stats count by ip_address, search_name
          ]
        | search NOT search_name=valid_ips

When doing this, remember to put search in the subsearch! Otherwise, it won't work at all.
Filtering

NOT v !=

This is so lame, and is such a gotcha. Original source.
Turns out, empty string is considered "not existing". Which means, if you have a column of either empty string, or value, and you want to get empty strings only, use NOT rather than !=.
Formatting

I like things looking nice. Often this also means better usability, as it takes less mental energy to parse output
meant for machines. However, Splunk is a terrible means to nicely format output, especially when trying to send
this output downstream (like JIRA).
Through lots of trial and error, I have found these patterns to work nicely:


Use rex to extract values


Use eval to assign temporary variables


Use mvexpand to split multiple results from rex into their own separate rows


Use stats list(<field_to_combine>) as <new_name_for_field> by <params_you_want_to_group_together>
to combine rows.


Use nomv to teach JIRA to recognize multi-value rows, then use rex to replace spaces with new lines.
IMPORTANT: Even though Splunk does not show the new lines, it will come out as expeected in JIRA!


Miscellaneous Gotchas

Using rename

For some wacky reason,
stats count by data.user as user

is not the same as
stats count by data.user | rename data.user to user

The latter works as expected. I guess learning this method is always better, since it also works
when trying to count by multiple items.
stats count by data.user, data.email | rename data.user to user

References


Useful other eval functions.