How can I use regex to remove anything between paragraphs?

Answer and Explanation

Removing content between paragraphs with a regular expression (regex) often involves identifying clear boundaries between paragraphs—such as double newlines in plain text or specific HTML tags in markup. Once those boundaries are defined, you can craft a pattern that targets (and removes) everything between them.

1. Plain Text Example

In plain text, paragraphs are typically separated by one or more blank lines. For instance, consider this text:

Lorem ipsum dolor sit amet, consectetur adipiscing elit.

This is the content you want to remove.

Sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.

To remove the content between these paragraphs, you can use a pattern with a lookbehind and lookahead that target double newlines. For example:

(?<=\n\n).*?(?=\n\n)

Explanation: The (?<=\n\n) part ensures the match is preceded by two newline characters, (.*?) performs a lazy match of any characters, and (?=\n\n) ensures the match is followed by two newline characters.

Below is a Python snippet demonstrating how to apply this pattern:

import re

text = """Lorem ipsum dolor sit amet, consectetur adipiscing elit.

This is the content you want to remove.

Sed do eiusmod tempor incididunt ut labore et dolore magna aliqua."""

pattern = r"(?<=\n\n).*?(?=\n\n)"
cleaned_text = re.sub(pattern, "", text, flags=re.DOTALL)

print(cleaned_text)

The resulting output removes the line between paragraphs, leaving only:

Lorem ipsum dolor sit amet, consectetur adipiscing elit.

Sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.

2. HTML Example

When dealing with HTML, paragraphs might be enclosed within  tags. Here’s a simple example:

First paragraph.

Content to remove.

Second paragraph.

To remove an entire paragraph (like the second one), a pattern that captures from  to  can be used:

.*?

Below is a JavaScript snippet demonstrating this in practice:

const htmlContent = `
First paragraph.
Content to remove.
Second paragraph.
`;

const regex = /.*?<\/p>/gs;
const cleanedHtml = htmlContent.replace(regex, '').trim();

console.log(cleanedHtml);

This removes all paragraphs by default, so to selectively remove only certain paragraphs, you would adjust your pattern to target specific keywords or content. For instance, to remove only paragraphs containing “remove,” you might look for .*?remove.*?.

Be cautious when applying regex to HTML. For larger or more complex HTML structures, an HTML parser is usually safer and more predictable.

3. Considerations and Best Practices

Use Non-Greedy Matching: Patterns like .*? ensure the smallest possible match, preventing unintended removals.

Enable the Correct Flags: In many languages, you may need flags (e.g., re.DOTALL in Python or the s flag in JavaScript) to let the dot (.) match newline characters.

Test Your Regex: Tools like Regex101 help verify that your pattern behaves as expected before deploying it to production.

Advanced Filters: If you only want to remove paragraphs that contain certain words (e.g., “remove”), you can include those terms within your capturing groups or lookarounds to specifically target content.

When Parsing HTML, Consider Parsers: While regex can handle simple HTML, using an HTML or DOM parser is often more robust when the structure is complex.

4. Advanced Example: Targeting Specific Keywords

Below is an example removing only paragraphs that contain the word “remove” in a plain text scenario:

import re

text = """First paragraph.

This content should be removed.

Second paragraph."""

pattern = r"(?<=\n\n).*?remove.*?(?=\n\n)"
cleaned_text = re.sub(pattern, "", text, flags=re.DOTALL | re.IGNORECASE).strip()

print(cleaned_text)

Notice that we used re.IGNORECASE to remove content regardless of whether “remove” is uppercase or lowercase.

Conclusion