Prepend certain lines of file

Question

I\'d like to create a script to comment out lines of my Mac OS X hosts file that contain .com. And also one to reverse it.

So this:

127.0.0.         


        

Answer 1

With awk

awk '$2 ~ /.com/{$0 = "#"$0;}{print}' temp.txt

Output

#127.0.0.1    foo.com
#127.0.0.1    bar.com
127.0.0.1    baz
127.0.0.1    qux