Initial commit

.gitignore

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+/target
+Cargo.lock
+*~

Cargo.toml

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+[package]
+name = "rematch"
+version = "0.1.0"
+authors = ["Avril <flanchan@cumallover.me>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+regex = "1"

src/main.rs

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+extern crate regex;
+use regex::Regex;
+
+fn main() {
+    let args: Vec<String> = std::env::args().collect();
+
+    if args.len() < 4 {
+	println!("Usage: {} <str> <regex> <group>", args[0]);
+    } else {
+	let re = Regex::new(&args[2]).unwrap();
+	let text = &args[1];
+	let group: usize = args[3].parse().expect("Invalid group number.");
+
+	let groups = re.captures(&text).unwrap();
+
+	if group > groups.len() {
+	    eprintln!("Invalid group number.");
+	} else {
+	    println!("{}", groups.get(group).unwrap().as_str());
+	}
+    }
+}