does ripgrep's regex engine follow a specification? and is it compatible with .NET's regex engine?

[Akash-Mair]

Hey regex noob here,

Im using both ripgrep and the Regex class from dotnet. I want to ensure that both are matching on the same input. Do you know if the regex crate that ripgrep uses is compatible with the regex engine dotnet uses?

Thank you :D

[BurntSushi]

It is not. AFAIK, .NET does not follow any spec. And ripgrep uses Rust's regex crate, and that doesn't follow any spec either. In general, there are only two broadly applicable regex specifications: POSIX and ECMAScript. AFAIK, .NET allows you to opt into ECMAScript if you wanted to. But both specifications require implementing features that are not known how to implement efficiently (such as look-around). In contrast, Rust's regex crate follows the RE2 tradition and specific eschews those features so that it can use finite automata as an implementation technique and guarantee worst case linear time searches.

Rust's regex crate syntax is documented here: https://docs.rs/regex/latest/regex/#syntax

You can also browse through the rebar benchmark suite for regex engines (which includes Rust's regex crate and .NET). Its "test" benchmarks specifically expose some differences. Here is one example of a difference.

Overall, if you stick to "simple" regexes, then they should generally behave the same. But there are likely a number of corner cases where behavior differs. And of course, .NET supports more stuff that Rust's regex crate. If you need to deal with that, then you can opt into using PCRE2 in ripgrep with the -P/--pcre2 flag. But there's no guarantee that PCRE2 matches what .NET does either.

[Akash-Mair]

Thank you so much!

[ltrzesniewski]

Just in case you need it, you can also use PCRE2 from .NET - I made PCRE.NET for this purpose.

[BurntSushi]

It would also be possible to use Rust's regex crate from .NET. It exposes a C API: https://github.com/rust-lang/regex/tree/master/regex-capi/ctest

I don't think anyone has written an ffi binding for .NET for it though. It probably wouldn't be too hard.