Question

I have a file like this:

foo, bar, foo1
bar, foo
foo

I want it like this:

foo
bar
foo1
bar
foo
foo

Answer 1

cat file | tr ' ' '\n' | tr -d , 

If you want to remove empty lines in the stream just add | grep -xv ''

If you mean that columns are separated with ,, you can use something like:

cat file.txt | sed 's/, /\n/g'

I must note that that will not work in Mac OS X (thanks to Frost for the tip).
When you are in Mac OS X, you must use another construction that is not so nice:

cat file.txt | sed -e 's/, /\'$'\n/g'