PHP single quotes in an echo

Use double quotes outside and simple inside:

$email = "[email protected]";
echo "mail->addAddress('$email');";

Demo

With the single quotes, print literals. With the doubles it prints the content and its variables.

Ex:

• echo '$email' print "$email"
• echo "$email" print "[email protected]"

You can also use the escape character as Diego says in his answer.

You can use the escape character /:

$email = "[email protected]";
echo 'mail->addAddress(\''.$email.'\')';

Or also using double quotes on the outside:

$email = "[email protected]";
echo "mail->addAddress('$email')";

Also, in this second example, you do not need to use concatenation, since PHP searches inside the chain if there are variables to print.