Regex Dotall Flag Example Explained

What is the Regex Dotall Flag

The dotall flag (sometimes called singleline flag) modifies regex behavior so that the dot (.) metacharacter matches any character including newlines. Normally, the dot matches any character except newline characters by default.

Basic Syntax and Usage

Most regex engines use syntax like:

re.DOTALL # Python

Pattern.DOTALL # Java

Pattern.S # Perl/Ruby

This flag changes how the dot character works in your regex patterns.

Practical Example Comparison

Here's a regex dotall flag example with sample text:

Sample text:

"Hello\

World"

Without dotall flag:

- Pattern: `H.llo` matches "Hello"

- Pattern: `H.World` does NOT match

With dotall flag:

- Pattern: `H.llo` matches "Hello"

- Pattern: `H.World` matches "Hello\

World"

Common Use Cases

The regex dotall flag is useful when:

- Extracting content between multi-line tags

- Matching text that spans multiple lines

- Processing log files with line breaks

Example: Extract all text between <note> tags

import re

pattern = re.compile(r'<note>(.*)</note>', re.DOTALL)