How to Capture Multiline Text Blocks with Regular Expressions?

Regular Expression for Matching Multiline Text Blocks

Matching text that spans multiple lines can present challenges in regular expression construction. Consider the following example text:

some Varying TEXT

DSJFKDAFJKDAFJDSAKFJADSFLKDLAFKDSAF
[more of the above, ending with a newline]
[yep, there is a variable number of lines here]

(repeat the above a few hundred times)

The goal is to capture two components: the "some Varying TEXT" part and all subsequent lines of uppercase text, excluding the empty line.

Incorrect Approaches:

Some incorrect approaches to solving this problem include:

• Using ^ and $ anchors to match linefeeds. In multiline mode, ^ matches positions following newlines and $ matches positions preceding newlines.
• Using the DOTALL modifier to match everything, which is unnecessary since the dot (.) matches everything except newlines.

Solution:

The following regular expression correctly captures the desired components:

^(.+)\n((?:\n.+)+)

Here's a breakdown of its components:

• ^ matches the start of the line.
• (. ) captures the "some Varying TEXT" part into group 1.
• n matches a newline character.
• ((?:n. ) ) captures all subsequent lines of uppercase text into group 2. The ?: non-capturing group construct prevents these lines from being captured as individual groups.
• The repetition operator ensures that at least one line of uppercase text is present.

Usage:

To use this regular expression in Python, you can use the following code:

<code class="python">import re

pattern = re.compile(r"^(.+)\n((?:\n.+)+)", re.MULTILINE)</code>

You can then use the match() method to find matches in a string:

<code class="python">match = pattern.match(text)
if match:
    text1 = match.group(1)
    text2 = match.group(2)</code>

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