are you connected with SSH or in the GNOME terminal?
either way open two terminal screens, vi the target and source files in each separate screen
in the source file if using SSH to connection you can highlight and COPY from Source.
in the TARGET go to line in which you want to insert, do a ESC "o' Lower case O to open a new line.
then "paste the content" of the clipboard from the source. with ESC p
OR
if you wish to place a specific line, you can also grep for the line in SOURCE and concat it at the end of target.
grep "String" source
to see if it pulls the string you want.
to append the "String" at the end of the target file
simply
grep "String" source >> Target
I do a lot of preprocessing of files between database on a linux box, there are a lot of ways to play it but a simple edit is using vi. get familiar with it and becomes a very good friend. A lot of NOOBs struggle with it, but it isn't as complicated