Interpolating Variables in Strings
As discussed earlier in this chapter, you can display the values of variables like this in PHP:
$sandwiches = 1; echo "Number of sandwiches: ", $sandwiches, ".";
However, there’s a shortcut that you can use here. The values in variables are interpolated if you put them into double-quoted (not single-quoted) strings, which means that their values are inserted directly into the string. You can do that this way to convert the example from the previous code:
$sandwiches = 1; echo "Number of sandwiches: $sandwiches.";
As you’d expect, this example displays Number of sandwiches: 1.
Here’s a more complete example of variable interpolation, interpolation.php:
<html> <head> <title> Interpolating variables with PHP </title> </head> <body> <h1> Interpolating variables with PHP </h1> <? echo "Setting number of sandwiches to 2.<br>"; $sandwiches = 2; echo "Number of sandwiches: $sandwiches <BR>"; echo "Adding 2 more sandwiches.<BR>"; $sandwiches = $sandwiches + 2; echo "Number of sandwiches now: $sandwiches <BR>"; ?> </body> </html>
You can see the results in Figure 12.6.
Figure 12.6: Using interpolation
Interpolating can be useful, but it should be used with caution. What if you wanted to interpolate a variable named $data containing the word hot to the text dog? That might look like this:
<? $data = "hot"; echo "Want a $datadog? <br>"; ?>
This is not going to work, however, because PHP is going to start looking for a variable named $datadog, as you see here:
PHP Notice: Undefined variable: datadog in hotdog.php on line 3
Instead, the way to do this is to enclose the variable you’re interpolating, $text, in curly braces, { and }, like this:
<html> <head> <title> Interpolating variables with PHP </title> </head> <body> <h1> Interpolating variables with PHP </h1> <? $data = "hot"; echo "Want a ${data}dog? <br>"; ?> </body> </html> You do indeed get Want a hotdog? from this example. In general, variable interpolation is a handy shortcut, and one you’ll see often in PHP.
