How to eval PHP code via drush without escaping quotes routine

Very often there is a need to execute via drush eval command the PHP code with both single and double quotes, something like this:

<?php
echo "Hello, '$username'!"; 
?>

This can be quickly done without manually adding slashes to each quote in PHP code via this bash trick:

PHP=`cat <<'EOF'
echo "Hello, '$username'!"; 
EOF`; drush ev "$PHP"

Instead of single line of PHP code, you can insert long multi-line part of code, without carrying about escaping quotes.