how to write finding output to same file using awk command

Question

awk \'/^nameserver/ && !modif { printf(\"nameserver 127.0.0.1\\n\"); modif=1 } {print}\' testfile.txt

It is displaying output but I want to wri

Answer 1

You can also use sponge from moreutils.

For example

awk '!a[$0]++' file|sponge file

removes duplicate lines and

 awk '{$2=10*$2}1' file|sponge file

multiplies the second column by 10.