如何在TextWrangler中使用grep用逗号替换换行符?

I have a text-file container a number of lines, which I need to turn into a csv. What is the easiest way to replace all the line-breaks with ", ". I have TextWrangler and read that it would do so by using grep and regular expressions, but have very little experience using regular expressions and don't know how grep works. Anyone who can help me get started?I have a text-file container a number of lines,