Insert lines in files with sed

How to insert lines into text files using stream editor (sed)

Q. How can I insert a line in a specific position in a text file?

A. You can use sed in order to add or insert a line in a specific position of a text file.

Let's say you have a file named, well file.txt and you want to insert a line in position 2, with this string Hello World.

The command should be:

sed '2i\'$'\n''Hello World'$'\n' file.txt

Now, as a bonus, let's see how to do it in a bunch of files.

for i in *.txt; do sed '2i\'$'\n''Hello World'$'\n' $i > tmp/$i ; done