Rust
正規表現

前書き

シンプルマッチと検索

tustのための正規表現のサポートは、によって提供されるregexあなたにそれを追加し、クレートCargo.toml ：

[dependencies]
regex = "0.1"

regex木枠の主なインターフェースはregex::Regexです：

extern crate regex;
use regex::Regex;

fn main() {
    //"r" stands for "raw" strings, you probably
    // need them because rustc checks escape sequences,
    // although you can always use "\\" withour "r"
    let num_regex = Regex::new(r"\d+").unwrap();
    // is_match checks if string matches the pattern
    assert!(num_regex.is_match("some string with number 1"));

    let example_string = "some 123 numbers";
    // Regex::find searches for pattern and returns Option<(usize,usize)>,
    // which is either indexes of first and last bytes of match
    // or "None" if nothing matched
    match num_regex.find(example_string) {
        // Get the match slice from string, prints "123"
        Some(x) => println!("{}", &example_string[x.0 .. x.1]),
        None    => unreachable!()
    }
}

キャプチャグループ

extern crate regex;
use regex::Regex;

fn main() {
    let rg = Regex::new(r"was (\d+)").unwrap();
    // Regex::captures returns Option<Captures>,
    // first element is the full match and others
    // are capture groups
    match rg.captures("The year was 2016") {
        // Access captures groups via Captures::at
        // Prints Some("2016")
        Some(x) => println!("{:?}", x.at(1)),
        None    => unreachable!()
    }

    // Regex::captures also supports named capture groups
    let rg_w_named = Regex::new(r"was (?P<year>\d+)").unwrap();
    match rg_w_named.captures("The year was 2016") {
        // Named capures groups are accessed via Captures::name
        // Prints Some("2016")
        Some(x) => println!("{:?}", x.name("year")),
        None    => unreachable!()
    }

}

置換

extern crate regex;
use regex::Regex;

fn main() {
    let rg = Regex::new(r"(\d+)").unwrap();

    // Regex::replace replaces first match 
    // from it's first argument with the second argument
    // => Some string with numbers (not really)
    rg.replace("Some string with numbers 123", "(not really)");

    // Capture groups can be accesed via $number
    // => Some string with numbers (which are 123)
    rg.replace("Some string with numbers 123", "(which are $1)");

    let rg = Regex::new(r"(?P<num>\d+)").unwrap();
    
    // Named capture groups can be accesed via $name
    // => Some string with numbers (which are 123)
    rg.replace("Some string with numbers 123", "(which are $num)");

    // Regex::replace_all replaces all the matches, not only the first
    // => Some string with numbers (not really) (not really)
    rg.replace_all("Some string with numbers 123 321", "(not really)");
}