Regex: Find and show only the string between FIRST-PART and SECOND-PART of the text

2 min read 19-10-2024

the ifix

Regex: Find and show only the string between FIRST-PART and SECOND-PART of the text

When working with text data, it is often necessary to extract specific portions of text based on certain delimiters. A common scenario is extracting the substring between two distinct markers, such as "FIRST-PART" and "SECOND-PART". In this article, we will explore how to achieve this using regular expressions (Regex) with practical examples.

The Problem Scenario

Imagine you have the following string of text:

"Here is the FIRST-PART This is the text you want to extract. SECOND-PART and here is more text."

You want to extract only the substring that appears between "FIRST-PART" and "SECOND-PART".

To clarify, our goal is to obtain:

"This is the text you want to extract."

The Original Code

Here’s a simple example of how you could write the Regex to achieve this using Python:

import re

text = "Here is the FIRST-PART This is the text you want to extract. SECOND-PART and here is more text."
pattern = r'FIRST-PART (.*?) SECOND-PART'

result = re.search(pattern, text)

if result:
    extracted_text = result.group(1)
    print(extracted_text)
else:
    print("No match found")

Explanation of the Code

Import the Regex Library: We start by importing Python's re library, which provides support for working with regular expressions.
Define the Text: We create a string variable text that contains our original sentence with "FIRST-PART" and "SECOND-PART".
Craft the Pattern: The Regex pattern r'FIRST-PART (.*?) SECOND-PART' is constructed to find text between "FIRST-PART" and "SECOND-PART":
- FIRST-PART: This part of the pattern matches the literal string "FIRST-PART".
- (.*?): This is a capturing group. The .*? means to match any character (.), zero or more times (*), in a non-greedy way (?). This allows us to capture everything in between our markers.
- SECOND-PART: This matches the literal string "SECOND-PART".
Search for the Pattern: We use re.search() to search the text for our defined pattern. If a match is found, result.group(1) retrieves the text captured by our first capturing group.
Output the Result: The extracted text is printed. If no match is found, it informs the user accordingly.

Practical Examples

Example 1: Email Extraction

Suppose you have email data and need to extract the username between "USER:" and "DOMAIN:". Using the same principle, you could modify the Regex pattern as follows:

email_text = "USER: john.doe DOMAIN: example.com"
pattern = r'USER: (.*?) DOMAIN:'

result = re.search(pattern, email_text)

if result:
    username = result.group(1)
    print(username)  # Output: john.doe
else:
    print("No match found")

Example 2: Log File Parsing

If you have log entries where you want to extract timestamps between the strings "[START]" and "[END]", you can use Regex in a similar fashion:

log_entry = "[START] 2023-10-05 10:00:00 [END] Some more log data."
pattern = r'\[START\] (.*?) \[END\]'

result = re.search(pattern, log_entry)

if result:
    timestamp = result.group(1)
    print(timestamp)  # Output: 2023-10-05 10:00:00
else:
    print("No match found")

Conclusion

Extracting strings between two markers using Regex is a powerful tool in text processing. It simplifies the task of pulling specific information from larger text blocks. Whether you are working with plain text, logs, or data formats like JSON and XML, regular expressions can save you time and effort.

For further learning, consider exploring the following resources:

RegexOne - A simple introduction to Regex.
Regex101 - A Regex tester and debugger.
Regular Expressions Info - In-depth tutorials and references.

Feel free to implement this technique in your text processing tasks, and leverage the power of Regex to enhance your data manipulation capabilities!