There are a few ways to achieve that:
1. sed
$ echo "one two three" | sed 's/ /\n/g'2. awk
one
two
three
$ echo "one two three" | awk '$1=$1' RS= OFS="\n"3. tr
one
two
three
$ echo "one two three" | tr -s ' ' '\n'3 ways to do it, have fun
one
two
three