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