mirror of
https://github.com/jbranchaud/til
synced 2026-01-19 23:18:01 +00:00
43 lines
1.5 KiB
Markdown
43 lines
1.5 KiB
Markdown
# Use Negative Lookbehind Matching With ripgrep
|
|
|
|
The most straightforward way to use `ripgrep` is to hand it a pattern. It will
|
|
take that pattern and move forward through each file trying to find matches.
|
|
|
|
```bash
|
|
$ rg 'TwilioClient\.new'
|
|
```
|
|
|
|
That will find all occurrences of `TwilioClient.new` in available project files.
|
|
|
|
What if that pattern is too permissive though? That is going to match on
|
|
occurrences of `TwilioClient.new` as well as things like
|
|
`LoggingTwilioClient.new`. If we want to exclude the latter, there are a few
|
|
ways to do that. One of them being the use of [the _negative lookbehind_ regex
|
|
feature](https://www.pcre.org/current/doc/html/pcre2syntax.html#SEC23) that is
|
|
available with PCRE2 (Perl-Compatible Regular Expressions).
|
|
|
|
A _negative lookbehind_ is like a standard pattern. We look forward through the
|
|
document for the base pattern (like `TwilioClient\.new`). However, once we find
|
|
that match, we then look back at the previous characters and if they match our
|
|
negative lookbehind pattern, then it is no longer a positive match.
|
|
|
|
We can use one of the following to forms to achieve this:
|
|
|
|
```
|
|
(?<!...) )
|
|
(*nlb:...) ) negative lookbehind
|
|
(*negative_lookbehind:...) )
|
|
```
|
|
|
|
For instance, here is what this looks like for our example:
|
|
|
|
```bash
|
|
$ rg -P '(?<!Logging)TwilioClient\.new'
|
|
```
|
|
|
|
Note: we have to use the `-P` flag to tell `ripgrep` that we are using PCRE2
|
|
syntax. Otherwise, it assumes a simpler regex syntax that doesn't support
|
|
_negative lookbehind_.
|
|
|
|
See `man rg` for more details.
|