You can put variables, object properties, and array elements (if the subscript is unquoted) directly in double-quoted strings:

<?php
print "I have $children children.";
print "You owe $amounts[payment] immediately.";
print "My circle's diameter is $circle->diameter inches.";
?>

Interpolation with double-quoted strings places some limitations on the syntax of what can be interpolated. In the previous example, $amounts['payment'] had to be written as $amounts[payment] so it would be interpolated properly. Use curly braces around more complicated expressions to interpolate them into a string. For example:

<?php
print "I have less than {$children} children.";
print "You owe {$amounts['payment']} immediately.";
print "My circle's diameter is {$circle->getDiameter()} inches.";
?>

Direct interpolation or using string concatenation also works with heredocs. Interpolating with string concatenation in heredocs can look a little strange because the closing heredoc delimiter and the string concatenation operator have to be on separate lines:

<?php
print <<< END
Right now, the time is
END
. strftime('%c') . <<< END
 but tomorrow it will be
END
. strftime('%c',time() + 86400);
?>

Also, if you’re interpolating with heredocs, make sure to include appropriate spacing for the whole string to appear properly. In the previous example, Right now the time has to include a trailing space, and but tomorrow it will be has to include leading and trailing spaces.