How to save command output to specific line of text file

I would like to know how to save command output to a specific line of a text file.

I searched on the internet for about an hour about this problem, but I didn't find any proper answer.

For example:

I want to save the output of some ls command to 7th line of example.txt. (insert new line)

How would I do it?

Thanks in advance.

You could use sed's r command to read and insert the command output after a given address. In particular, GNU sed provides the special filename /dev/stdin to read data from standard input.

So for example, given

$ cat example.txt
Line 1
Line 2
Line 3
Line 4
Line 5
Line 6
Line 7
Line 8
Line 9
Line 10

then

$ ls -l example.txt | sed -i '7r/dev/stdin' example.txt

results in

$ cat example.txt
Line 1
Line 2
Line 3
Line 4
Line 5
Line 6
Line 7
-rw-r--r-- 1 steeldriver steeldriver 71 Jun 28 15:52 example.txt
Line 8
Line 9
Line 10

If you want the command output inserted before the 7th line, then read and insert it after the 6th.