Since you already have all your file words in an array, then you can do like so:

  print join ',' => @names12;
[download]

This would print out all your data follow with a comma. See: the use of join

However, I would not do it this way, since you are going through the file, line by line, there is no need to store that the words after slitting.
You can simply split and print at once like so: (Using your code.)

      while(<MYFILE>){
        chomp;
        print join ',' => split;
      }
[download]

Update:
Please, use warnings and strict in your code.
Also use autodie or check the return status of function open.
Using a three argument of open function is also encouraged.