Replacing Newline with Space

Let's say we have a list of words like below

$ cat animals

cat

fish

zebra

monkey

and we want it to be arranged in one horizontal line, separated by space. We can achieve that by using tr command.

$ cat animals | tr "\n" " " 

cat fish zebra monkey

What happened is, \n (symbol for newline), will be replaced with " ", which is symbol for space.