1    2            2        5                4
4    4    4            4                3    
0        4    4            1                
0    1    5    6        4                    



#!/usr/bin/perl

# https://perlmonks.org/?node_id=1220510

use strict;
use warnings;


open(DATA,"DATA")||die"cannot open the file: $!\n";


while( <DATA> )
  {
  s/(^|    \K)(?!\d)/0/g;
  print;
  }