The UNIX tr command
$> tr ',' '\012' <> return.txt
tr is the program doing the work.
',' is the character I want to replace (in this case a comma).
'\012' is the octal value for a newline in UNIX.
comma .txt is the file I am reading from.
return.txt is the new file I am saving my changes to.
from : http://www.flashcodersny.org/wordpress/?p=19