GrepUtil.java

import java.io.BufferedReader;
import java.io.Reader;
import java.util.Arrays;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.stream.Stream;

public class GrepUtil {

    public static Stream<String> grep(Reader reader, String... words) {

        AtomicInteger index = new AtomicInteger();
        return new BufferedReader(reader).lines()
                .map(s -> new GrepFile(index.incrementAndGet(), s))
                .filter(o -> Arrays.asList(words).stream().anyMatch(s -> o.getWord().contains(s)))
                .map(o -> o.toString());
    }

    static class GrepFile {
        private int index;
        private String word;

        public GrepFile(int index, String word) {
            this.index = index;
            this.word = word;
        }

        public String getWord() {
            return word;
        }

        public String toString() {
            return index + ": " + word;
        }
    }
}