A Rust library for parsing, compiling, and executing regular expressions. Its syntax is similar to Perl-style regular expressions, but lacks a few features like look around and backreferences. In exchange, all searches execute in linear time with respect to the size of the regular expression and search text. Much of the syntax and implementation is inspired by RE2.
Module documentation with examples. The module documentation also includes a comprehensive description of the syntax supported.
Documentation with examples for the various matching functions and iterators
can be found on the
To bring this crate into your repository, either add
regex to your
Cargo.toml, or run
cargo add regex.
Here's a simple example that matches a date in YYYY-MM-DD format and prints the year, month and 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; const TO_SEARCH: &'static str = " On 2010-03-14, foo happened. On 2014-10-14, bar happened. ";
This example outputs:
year: 2010, month: 03, day: 14 year: 2014, month: 10, day: 14
Usage: Avoid compiling the same regex in a loop
It is an anti-pattern to compile the same regular expression in a loop since compilation is typically expensive. (It takes anywhere from a few microseconds to a few milliseconds depending on the size of the regex.) Not only is compilation itself expensive, but this also prevents optimizations that reuse allocations internally to the matching engines.
In Rust, it can sometimes be a pain to pass regular expressions around if
they're used from inside a helper function. Instead, we recommend using the
lazy_static crate to ensure that
regular expressions are compiled exactly once.
Specifically, in this example, the regex will be compiled when it is used for the first time. On subsequent uses, it will reuse the previous compilation.
Usage: match regular expressions on
The main API of this crate (
regex::Regex) requires the caller to pass a
&str for searching. In Rust, an
&str is required to be valid UTF-8, which
means the main API can't be used for searching arbitrary bytes.
To match on arbitrary bytes, use the
regex::bytes::Regex API. The API
is identical to the main API, except that it takes an
&[u8] to search
on instead of an
&str. By default,
. will match any byte using
. will match any UTF-8 encoded Unicode scalar
value using the main API.
This example shows how to find all null-terminated strings in a slice of bytes:
use Regex; let re = new.unwrap; let text = b"foo\x00bar\x00baz\x00"; // Extract all of the strings without the null terminator from each match. // The unwrap is OK here since a match requires the `cstr` capture to match. let cstrs: = re.captures_iter .map .collect; assert_eq!;
Notice here that the
[^\x00]+ will match any byte except for
using the main API,
[^\x00]+ would instead match any valid UTF-8 sequence
Usage: match multiple regular expressions simultaneously
This demonstrates how to use a
RegexSet to match multiple (possibly
overlapping) regular expressions in a single scan of the search text:
use RegexSet; let set = new.unwrap; // Iterate over and collect all of the matches. let matches: = set.matches.into_iter.collect; assert_eq!; // You can also test whether a particular regex matched: let matches = set.matches; assert!; assert!;
Usage: enable SIMD optimizations
SIMD optimizations are enabled automatically on Rust stable 1.27 and newer. For nightly versions of Rust, this requires a recent version with the SIMD features stabilized.
Usage: a regular expression parser
This repository contains a crate that provides a well tested regular expression parser, abstract syntax and a high-level intermediate representation for convenient analysis. It provides no facilities for compilation or execution. This may be useful if you're implementing your own regex engine or otherwise need to do analysis on the syntax of a regular expression. It is otherwise not recommended for general use.
This crate comes with several features that permit tweaking the trade off between binary size, compilation time and runtime performance. Users of this crate can selectively disable Unicode tables, or choose from a variety of optimizations performed by this crate to disable.
When all of these features are disabled, runtime match performance may be much
worse, but if you're matching on short strings, or if high performance isn't
necessary, then such a configuration is perfectly serviceable. To disable
all such features, use the following
Cargo.toml dependency configuration:
 = "1.3" = false # regex currently requires the standard library, you must re-enable it. = ["std"]
This will reduce the dependency tree of
regex down to a single crate
The full set of features one can disable are in the "Crate features" section of the documentation.
Minimum Rust version policy
This crate's minimum supported
rustc version is
The current tentative policy is that the minimum Rust version required
to use this crate can be increased in minor version updates. For example, if
regex 1.0 requires Rust 1.20.0, then regex 1.0.z for all values of
also require Rust 1.20.0 or newer. However, regex 1.y for
y > 0 may require a
newer minimum version of Rust.
In general, this crate will be conservative with respect to the minimum supported version of Rust.
This project is licensed under either of
- Apache License, Version 2.0, (LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0)
- MIT license (LICENSE-MIT or https://opensource.org/licenses/MIT)
at your option.
The data in
regex-syntax/src/unicode_tables/ is licensed under the Unicode