How can I count FOUR letter word in a file
With a script. (What is the question such the answer.)
consider a file is written with this
There are three cats
Cats colour is white
Dogs always attack cats
With a shell script I want to filter out file like this
Cats
Cats
Dogs Cats
- What script language do you prefer?
- How many chars are in this "" or this ""?
- What did you try by yourself?
hmm, seems like homework 
I was about the post the answer :), but I will hold off, I guess the OP should give us a sample of what he tried.