Adding # before a line using csh

Shell Programming and Scripting
1

Hi,

I want to grep a word say "fan" from a file and redirect those lines in a file with "#" before them.

eg

all

fan is on
i am you
you are me
i am on fan

Expected o/p
#fan is on
#i am on fan

2 
sed -n '/fan/s/^/#/p' origfile > newfile
3

With awk...

awk '/fan/{$0="#"$0;print}' file