created_at2023-02-28 19:28:27.939514
updated_at2023-10-15 13:24:22.114887
descriptionA lightweight regex engine that optimizes for binary size and compilation time.
Andrew Gallant (BurntSushi)




This crate provides a lightweight regex engine for searching strings. The regex syntax supported by this crate is nearly identical to what is found in the regex crate. Like the regex crate, all regex searches in this crate have worst case O(m * n) time complexity, where m is proportional to the size of the regex and n is proportional to the size of the string being searched.

Build status



To bring this crate into your repository, either add regex-lite to your Cargo.toml, or run cargo add regex-lite.

Here's a simple example that matches a date in YYYY-MM-DD format and prints the year, month and day:

use regex_lite::Regex;

fn main() {
    let re = Regex::new(r"(?x)
(?P<year>\d{4})  # the year
(?P<month>\d{2}) # the month
(?P<day>\d{2})   # the day
    let caps = re.captures("2010-03-14").unwrap();

    assert_eq!("2010", &caps["year"]);
    assert_eq!("03", &caps["month"]);
    assert_eq!("14", &caps["day"]);

If you have lots of dates in text that you'd like to iterate over, then it's easy to adapt the above example with an iterator:

use regex::Regex;

const TO_SEARCH: &'static str = "
On 2010-03-14, foo happened. On 2014-10-14, bar happened.

fn main() {
    let re = Regex::new(r"(\d{4})-(\d{2})-(\d{2})").unwrap();

    for caps in re.captures_iter(TO_SEARCH) {
        // Note that all of the unwraps are actually OK for this regex
        // because the only way for the regex to match is if all of the
        // capture groups match. This is not true in general though!
        println!("year: {}, month: {}, day: {}",

This example outputs:

year: 2010, month: 03, day: 14
year: 2014, month: 10, day: 14

Minimum Rust version policy

This crate's minimum supported rustc version is 1.65.0.

The policy is that the minimum Rust version required to use this crate can be increased in semver compatible updates.


The primary purpose of this crate is to provide an alternative regex engine for folks that are unhappy with the binary size and compilation time of the primary regex crate. The regex-lite crate does the absolute minimum possible to act as a drop-in replacement to the regex crate's Regex type. It avoids a lot of complexity by choosing not to optimize searches and to opt out of functionality such as robust Unicode support. By keeping the code simpler and smaller, we get binary sizes and compile times that are substantially better than even the regex crate with all of its features disabled.

To make the benefits a bit more concrete, here are the results of one experiment I did. For regex, I disabled all features except for std:

  • regex 1.7.3: 1.41s compile time, 373KB relative size increase
  • regex 1.8.1: 1.46s compile time, 410KB relative size increase
  • regex 1.9.0: 1.93s compile time, 565KB relative size increase
  • regex-lite 0.1.0: 0.73s compile time, 94KB relative size increase

The main reason why regex-lite does so much better than regex when all of regex's features are disabled is because of irreducible complexity. There are certain parts of the code in regex that can't be arbitrarily divided based on binary size and compile time goals. It's instead more sustainable to just maintain an entirely separate crate.

Ideas for improving the binary size and compile times of this crate even more are most welcome.


This project is licensed under either of

at your option.

The data in regex-syntax/src/unicode_tables/ is licensed under the Unicode License Agreement (LICENSE-UNICODE).

Commit count: 1490

cargo fmt