[CentOS] Problems with my simple write conf files method

I have been creating conf files and similar with the following method 
that I picked up (I think from psotfix docs):

cat <<EOF>>/etc/aliases || exit 1
root: youremail
EOF

See: http://medon.htt-consult.com/Centos7-armv7.html

But with postfixadmin I stumbled onto a problem.  The following:

cat <<EOF>/usr/share/postfixadmin/config.local.php || exit 1
<?php
$CONF['database_type'] = 'mysqli';
$CONF['database_user'] = 'postfix';
$CONF['database_password'] = 'xyz';
$CONF['database_name'] = 'postfix';

$CONF['configured'] = true;
?>
EOF

produces:

cat <<EOF>/usr/share/postfixadmin/config.local.php || exit 1
<?php
['database_type'] = 'mysqli';
['database_user'] = 'postfix';
['database_password'] = 'xyz';
['database_name'] = 'postfix';

['configured'] = true;
?>

That is the '$CONF' gets processed.

What can I do to avoid this (and any other 'gotchas') or can someone 
provide an alternative?

thanks