write to specific line in file?

[globalrev]

i ahve a program that takes certain textsnippets out of one file and
inserts them into another.

problem is it jsut overwrites the first riow every time.

i want to insert every new piece of text into the next row.
so:
1. how do i write to a new line every time i write to the file?

2. if i dont want to write to a new line but just want to insert it
after the last token in the file, how do i do then?