I know charwise positions of matches like 1 3 7 8. I need to know their corresponding line number.

Example: file.txt

Match: X

Mathes: 1 3 7 8.

Want: 1 2 4 4

$ cat file.txt
X2
X
4
56XX

[Added: does not notice many linewise matches, there is probably easier way to do it with stacks]

$ java testt     
1
2
4
$ cat testt.java 
import java.io.*;
import java.util.*;
public class testt {

    public static String data ="X2\nX\n4\n56XX";
    public static String[] ar = data.split("\n");

    public static void main(String[] args){
        HashSet<Integer> hs = new HashSet<Integer>();
        Integer numb = 1;
        for(String s : ar){
            if(s.contains("X")){
                hs.add(numb);
                numb++;
            }else{
                numb++;
            }
        }   
        for (Integer i : hs){
            System.out.println(i);
        }
    }
}