Append characters at the end of each line. You can also append characters like new line or carriage return. I used in rsyslog configurations where I had scripted and created a set of remote syslog reception for a set of switches and needed the add the ending character for the if condition of syslog.

Append_Line-end

#!/bin/bash

sed -e 's/$/string after each line/' -i filename
#So for me I needed to add "& ~"  at the end of all lines in my file so that I could copy it to rsyslog.conf to receive logs from the network devices.
#Initial File:
if      $fromhost-ip    ==      '1.1.1.1'    then    /var/log/Switches/Switch1.log
if      $fromhost-ip    ==      '2.2.2.2'    then    /var/log/Switches/Switch2.log
.       .               .         .           .       .
.       .               .         .           .       .
.       .               .         .           .       .

#So I need to add "& ~" and a new line character to the next line of all the lines.
sed -e 's/$/\n\& \~\n/'  syslogfile