// strings/JGrep.java
// (c)2021 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.
// A very simple version of the "grep" program
// {java JGrep
// WhitherStringBuilder.java 'return|for|String'}
import java.util.regex.*;
import java.nio.file.*;
import java.util.stream.*;

public class JGrep {
  public static void
  main(String[] args) throws Exception {
    if(args.length < 2) {
      System.out.println(
        "Usage: java JGrep file regex");
      System.exit(0);
    }
    Pattern p = Pattern.compile(args[1]);
    // Iterate through the lines of the input file:
    int index = 0;
    Matcher m = p.matcher("");
    for(String line :
        Files.readAllLines(Paths.get(args[0]))) {
      m.reset(line);
      while(m.find())
        System.out.println(index++ + ": " +
          m.group() + ": " + m.start());
    }
  }
}
/* Output:
0: for: 4
1: for: 4
*/