Inserting #' to a configuration file using sed

Question

I'm trying to use sed to insert a # to a configuration file. I've tried:

sed 's/33/#' /path/to/file 

But get the output

sed: -e expression #1, char 6: unterminated `s' command

I've also tried

sed -i '33i#' /path/to/file

Which adds the # into line 33, but moves the text I want to comment down one line.

Can anyone point me in the right direction?

Answer 1

The solution you're after is:

sed -i '33s/^/#/' /path/to/file