Quick Answer
The answer is the `rex` command. This is correct because `rex` is specifically designed for extracting fields with regular expressions from raw event data without altering the original logs, making it ideal for parsing patterns like `[error_code: 404]` into a new field such as `error_code`. On the Splunk Core Certified User SPLK-1002 exam, this question tests your understanding of field extraction commands and their side effects—a common trap is confusing `rex` with `eval` or `extract`, which either modify data or rely on predefined key-value pairs. Remember, `rex` leaves the source untouched while `eval` creates or changes fields based on calculations. For this scenario, the regex `\[error_code: (?<field>\d+)\]` captures the numeric value between brackets, and `rex` applies it without rewriting the event. A helpful memory tip: think of `rex` as the "regex extractor"—it reads the pattern and pulls out what you need, leaving everything else exactly as it was.
This SPLK-1002 practice question tests your understanding of using fields and lookups. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
An administrator needs to extract a field from log data where the value appears between two square brackets, for example [error_code: 404]. Which search command should they use to create a custom field extraction without modifying the original data?
eval
Why wrong: eval can create fields but is not optimized for extraction from raw text.
fields
Why wrong: fields only includes or excludes fields, it does not create new ones.
extract
Why wrong: Extract is a legacy command for field extractions from dashboards, not for custom regex extraction.
rex
rex extracts fields using regex patterns without modifying the original data.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
rex
The `rex` command is used to extract fields using regular expressions without modifying the raw event data. In this scenario, `rex` can parse the pattern `\[error_code: (?<field>\d+)\]` to capture the value between square brackets into a new field, leaving the original log intact.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
eval
Why it's wrong here
eval can create fields but is not optimized for extraction from raw text.
fields
Why it's wrong here
fields only includes or excludes fields, it does not create new ones.
extract
Why it's wrong here
Extract is a legacy command for field extractions from dashboards, not for custom regex extraction.
rex
Why this is correct
rex extracts fields using regex patterns without modifying the original data.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Splunk often tests the distinction between `extract` (for key-value pairs) and `rex` (for regex-based extraction), and the trap here is that candidates confuse `extract` with general field extraction, not realizing it requires a specific `field=value` format to work.
Trap categories for this question
Command / output trap
Extract is a legacy command for field extractions from dashboards, not for custom regex extraction.
Detailed technical explanation
Under the hood, `rex` applies a PCRE (Perl Compatible Regular Expression) to the `_raw` field by default, capturing named groups into new fields. A subtle behavior is that `rex` can also be used with the `mode=sed` option for search-and-replace, but for extraction, the default mode creates fields from named capture groups. In real-world scenarios, this is critical for parsing semi-structured logs like HTTP access logs or custom application errors where values are enclosed in brackets.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
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Using Fields and Lookups — study guide chapter
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FAQ
Using Fields and Lookups — This question tests Using Fields and Lookups — Read the scenario before looking for a memorised answer..
The correct answer is: rex — The `rex` command is used to extract fields using regular expressions without modifying the raw event data. In this scenario, `rex` can parse the pattern `\[error_code: (?<field>\d+)\]` to capture the value between square brackets into a new field, leaving the original log intact.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 30, 2026
This SPLK-1002 practice question is part of Courseiva's free Splunk certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the SPLK-1002 exam.
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