How could I include a variable in a here document?

Question

I am trying to use a user-defined global variable in a cat <<eof>> filename situation, but it's not working. I found what I want in simple cat << eof examples on this forum, which led me here: http://www.tldp.org/LDP/abs/html/here-docs.html. But I would like to to something like the following, with the added >> and filename (This does not work.):

#!/bin/bash

#after testing I will define this in .bashrc or somewhere?
set IP_ADDR = "123.123.123.123"

#empty the file in case there is something in it
truncate -s 0 sample.conf

# open a file and append
cat <<EOF >> sample.conf
  This is my sample config file
  Server IP = $IP_ADDR
  this is the last line of my sample config file
EOF

#print the file to verify
cat sample.conf

This produces a null string after Server IP =

sed would work if I already had the file written except for the missing variable value, but I won't necessarily have the IP address (or whatever) readily available as a literal string.

Also, I might not have the literal string available for use as a command line parameter when I run the script. $1 does work within the cat << eof >> filename code block. I proved that. But I won't have immediate access to the value when I start this script...

Answer 1

set IP_ADDR = "123.123.123.123"

is incorrect. You need:

IP_ADDR="123.123.123.123"

(without spaces).