Question

I can grap a specific line from a file using sed. Is there an easy way to take this line or paragraph and insert onto a specific line in another file?

sed -n 1,10p >> foo appends the result to foo, which places it at the bottom. Is there a standard unix tool to insert onto a specific line?

Answer 1

Perhaps you are looking for sed‘s r command?

sed '123r file.txt' main.txt

inserts the contents of file.txt at line 123 of main.txt, printing everything to standard output.

(If your sed has the -i option, you can make it modify main.txt directly; otherwise, it will not modify its input files.)