// 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)})*)\}").unwrap();
let string = "\\int_{1}^{2}\\frac{x}{x/2}+{\\frac{\\sqrt{81}}{7x}}^7
\\int x
\\int_{19{} cz }^{2}{\\frac{x}{x/2}+7}+7
(\\int_{1}^{2}\\frac{x}{x/2})/2";
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/