What does sed -i option do?

Question

I\'m debugging a shell script and trying to find out the task performed by the following command:

sed -i \'1,+999d\' /home/org_user/data.txt

I

Answer 1

If -i option given, sed edit files in place.

   -i[SUFFIX], --in-place[=SUFFIX]

          edit files in place (makes backup if extension supplied)

from sed(1)

http://www.gnu.org/software/sed/manual/sed.html#Introduction