Hi Team, Please check this below: ~$ cat /etc/os-release NAME="Ubuntu" VERSION="14.04.5 LTS, Trusty Tahr" ID=ubuntu ID_LIKE=debian PRETTY_NAME="Ubuntu 14.04.5 LTS" VERSION_ID="14.04" HOME_URL="http://www.ubuntu.com/" SUPPORT_URL="http://help.ubuntu.com/" BUG_REPORT_URL="http://bugs.launchpad.net/ubuntu/" ~$ sed --version sed (GNU sed) 4.2.2 Copyright (C) 2012 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later . This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. Written by Jay Fenlason, Tom Lord, Ken Pizzini, and Paolo Bonzini. GNU sed home page: . General help using GNU software: . E-mail bug reports to: . Be sure to include the word ``sed'' somewhere in the ``Subject:'' field. Problem reproduce process: ~$ cat testfile 127.0.0.1 localhost hostname ::1 localhost ip6-localhost ip6-loopback The below command works as expected. ~$ sed -e 's/127.0.0.1/127/' -e "1i 127.0.0.1 localhost\n127.0.0.1 $HOSTNAME.domainname $HOSTNAME" testfile 127.0.0.1 localhost 127.0.0.1 node1.domainname node1 127 localhost hostname ::1 localhost ip6-localhost ip6-loopback But command below is not working as expeced: ~$ sed -e '/127.0.0.1/d' -e "1i 127.0.0.1 localhost\n127.0.0.1 $HOSTNAME.domainname $HOSTNAME" testfile ::1 localhost ip6-localhost ip6-loopback expected output: 127.0.0.1 localhost 127.0.0.1 node1.domainname node1 ::1 localhost ip6-localhost ip6-loopback If I add a comment at first line. then it's working. ~$ cat testfile # comment 127.0.0.1 localhost hostname ::1 localhost ip6-localhost ip6-loopback ~$ sed -e '/127.0.0.1/d' -e "1i 127.0.0.2 localhost\n127.0.0.2 $HOSTNAME.domainname $HOSTNAME" testfile 127.0.0.2 localhost 127.0.0.2 node1.domainname node1 # comment ::1 localhost ip6-localhost ip6-loopback