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 <http://gnu.org/licenses/gpl.html>.
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: <http://www.gnu.org/software/sed/>.
General help using GNU software: <http://www.gnu.org/gethelp/>.
E-mail bug reports to: <bug-sed@gnu.org>.
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