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:

import re

pattern = re.compile(r"^(. )\n((?:\n. ) )", re.MULTILINE)

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

match = pattern.match(text)
if match:
    text1 = match.group(1)
    text2 = match.group(2)