added feature "perl": use pcre

Cargo.toml

@@ -6,5 +6,9 @@ edition = "2018"
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
+[features]
+perl = ["pcre"]
+
 [dependencies]
-regex = "1"
+regex = "1"
+pcre = { version = "0.2.3", optional = true }

src/main.rs

@@ -1,6 +1,10 @@
+#[cfg(not(feature = "perl"))]
 extern crate regex;
+
+#[cfg(not(feature = "perl"))]
 use regex::Regex;
 
+#[cfg(not(feature = "perl"))]
 fn main() {
     let args: Vec<String> = std::env::args().collect();
 
@@ -11,12 +15,42 @@ fn main() {
 	let text = &args[1];
 	let group: usize = args[3].parse().expect("Invalid group number.");
 
-	let groups = re.captures(&text).unwrap();
+	match re.captures(&text) {
 
-	if group > groups.len() {
+	    Some(groups) => {
-	    eprintln!("Invalid group number.");
+		if group > groups.len() {
-	} else {
+		    eprintln!("Invalid group number.");
-	    println!("{}", groups.get(group).unwrap().as_str());
+		} else {
+		    println!("{}", groups.get(group).unwrap().as_str());
+		}
+	    }
+	    None => (),
 	}
     }
 }
+
+#[cfg(feature = "perl")]
+extern crate pcre;
+
+#[cfg(feature = "perl")]
+use pcre::Pcre;
+
+#[cfg(feature = "perl")]
+fn main () {
+    let args: Vec<String> = std::env::args().collect();
+
+    if args.len() < 4 {
+	println!("Usage: {} <str> <regex> <group>", args[0]);
+    } else {
+	let mut re = Pcre::compile(&args[2]).expect("Invalid regex.");
+	let text = &args[1];
+	let group: usize = args[3].parse().expect("Invalid group number.");
+
+	match re.exec(&text) {
+
+	    Some(m) if m.string_count() > group => println!("{}", m.group(group)),
+	    _ => (),
+	}
+    }
+}
+