Regex

The regex crate provides linear-time regex matching (no catastrophic backtracking like some engines).

Recipe

[dependencies]
regex = "1"

use regex::Regex;
 
fn main() {
    let re = Regex::new(r"^\d+$").unwrap();
    println!("{}", re.is_match("8080"));
}

When to reach for this: Log parsing, validation, extraction - prefer parse for simple numbers.

Working Example

use regex::Regex;
 
fn extract_ports(log: &str) -> Vec<u16> {
    let re = Regex::new(r"port=(\d+)").unwrap();
    re.captures_iter(log)
        .filter_map(|c| c.get(1)?.as_str().parse().ok())
        .collect()
}
 
fn main() {
    let log = "port=8080 ok\nport=3000 ok";
    println!("{:?}", extract_ports(log));
}

What this demonstrates:

• Compile regex once, reuse
• captures_iter for groups
• Combine with parse for typed output

Deep Dive

RegexBuilder for case insensitive, size limits. LazyLock static regex for global patterns.

Gotchas

• Compile in hot loop - Slow. Fix: LazyLock or once_cell.
• unwrap Regex::new - Invalid pattern panics at runtime. Fix: ? in fn returning Result.
• Regex for HTML/XML - Fragile. Fix: Proper parser.
• Overlapping matches - find_iter non-overlapping only.
• Unicode classes - \w Unicode-aware - mind performance.

Alternatives

FAQs

Related

• Parsing & Conversion
• String Manipulation
• Input Validation
• clap

Stack versions: This page was written for Rust 1.97.0 (edition 2024), Tokio 1.x, Axum 0.8, serde 1.0, sqlx 0.8, clap 4, and Polars 0.46+.