// include the latest version of the regex crate in your Cargo.toml
extern crate regex;
use regex::Regex;
fn main() {
let regex = Regex::new(r"(?m)^(?=.{1,20}$)(?=.*。)(?!.*，)([^。]*)。").unwrap();
let string = "<h1>这是一个测试。<h1>
这是一个测试，这是一个测试而已，希望去掉不需要的。
测试。
这是一个测试，这是一个测试而已，希望去掉不需要的第二行。
这是一行非常长的文字但是句号不需要被移除。";
let substitution = "$1";
// result will be a String with the substituted value
let result = regex.replace_all(string, substitution);
println!("{}", result);
}
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for Rust, please visit: https://docs.rs/regex/latest/regex/