I have tried everything I can think of to get sed to change line N of a file to the contents of a variable. I have Googled the Internet, and I find lots of people telling how to use variables with the "Substitute" command, but no one telling how to use variables with the "Change" command.

I have considered the possibility of using the "Substitute" command with a wild card for existing text, but my search of the Internet tells me SED doesn't have wild cards in its repertoire, so it's difficult! There must be a better way.

As I noted in the subject, the basic form I used is (where N is a line number):

sed -i 'N c\$variable' FILE

Use double quotes, single quotes prevent the shell to expand the variable:

sed -i "N c $variable" FILE

sed  "N c $variable" FILE

Yes!! It works! Thank you Franklin (and devtakh)! What an relief--better than a Christmas present!

This is really a surprise to me because I assumed the hard quote configuration was "cast in concrete". I'll have to admit, though, that my conclusions came from reading various comments during my Internet search on "sed". The manual itself is pretty vague on this subject. Now, in retrospect, I see that at the end of the manual there is reference to the sed website where the problem of variables is discussed at length! If I'd seen that in the first place, I probably could have figured it out, and not wasted the space on the Forum.

But you didn't even use the "\"!!! That I wouldn't have concluded from the manual. I guess it proves how many ways there are of doing things. I'm going to go back to the sed website and do some more study. I am sure thankful for the function that "sed" provides.

By the way, was I ever also wide-eyed when I found out about Zenity, after seeing it referenced on the web, and then discovered it was already installed! Amazing!

Thanks again very much.
Lauren.

First, -i option was not supported, so the above sed -i "N c $var " datafile is not portable.
Second, even if the -i option is not provided, using sed -i "N c[\] $var" datafile, still it cannot work.
The solution might be,
sed "N c\\
$var" datafile
which I tested under Solaris.

John, Hong

p.s.
sed "N s/.*/$var/" datafile also works out.