Regex101 to Grep/egrep returns nothing

I've been playing with the following regex to cut some content from a markdown file for me which works great in regex101 but can't seem to get grep to work with it. Either it errors or doesn't return anything The Regex is here: https://regex101.com/r/XDImM9/1 or (?s)##\s\[v0.0.1].+?(?=---) I've tried using grep with the -P flag which should support PCRE style regex but doesn't seem to do much grep -P 'm/(?s)##\s\[v0.0.1].+?(?=---)/' CHANAGELOG.md The sample data I have been working on is

# Changelog

All notable changes to this project will be documented in this file.
Please note that all entries must end with --- to allow for the auto release body to  use the Changelog



## [v0.0.1]

### Added
- Initial Commit/Release
---