How to edit a file via bash linux?

Question

linux

Good afternoon.
There was a need through ssh to edit the file. Open it, insert 50 lines in a certain place and close it, saving it. It would seem a simple task, but I didn’t see anything on the Internet other than the sed command. And this command gives me an error:

sed: -e expression #1, char 2: extra characters after command

Are there any other commands?