use strict;
use warnings;

open (NEW, ">", "OUTPUT_COMMA.txt" ) or die "could not open:$!";
open (FILE, "<", "INPUT.txt") or die "could not open:$!";

	while (my $line = <FILE>)
	{
    		$line =~s/\s{3} +/,/g;   
    		print NEW $line;

}
close (FILE);
close (NEW)