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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 ---
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2 Answers 2

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The two main issues I see here are:

  1. The enclosing m/ and / are regular expression delimiters – they should not be included as part of the regular expression itself.

  2. grep is line-oriented by default, so it doesn't really do multi-line matching. At least in GNU grep, you can use null byte delimiting to kludge it, by adding the -z flag.

So for example,

$ grep -zPo '(?s)##\s\[v0.0.1].+?(?=---)' CHANGELOG.md ## [v0.0.1] ### Added - Initial Commit/Release

For multi-line matching, you might consider using pcregrep if it is available for your platform, i.e.

pcregrep -Mo '(?s)##\s\[v0.0.1].+?(?=---)' CHANGELOG.md
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  • Cheers will just use the pcregrep, its only for a build container so easy enough to add to it. Commented Dec 19, 2019 at 0:22
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You have to remove m// delimiter, so :

grep -P '(?s)##\s\[v0.0.1].+?(?=---)' CHANAGELOG.md

But is not suited to be in multi-line mode by default, like in your regex101 snippet.

So, to the rescue :

perl -0 -lne 'print $& if m/(?s)##\s\[v0.0.1].+?(?=---)/' file

Output

## [v0.0.1] ### Added - Initial Commit/Release
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  • Yeah have tried that, still returns nothing. Commented Dec 19, 2019 at 0:14
  • POST edited with perl's solution (multiline mode) Commented Dec 19, 2019 at 0:17

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