How can I manually interpolate a string? [duplicate]

Question

The only way I've found to interpolate a string (that is, expand the variables inside it) is the following:

$str = 'This is a $a';
$a = 'test';
echo eval('return "' . $str . '";');

Keep in mind that in a real-life scenario, the strings are created in different places, so I can't just replace 's with "s.

Is there a better way for expanding a single-quoted string without the use of eval()? I'm looking for something that PHP itself provides.

Please note: Using strtr() is just like using something like sprintf(). My question is different than the question linked to in the possible duplicate section of this question, since I am letting the string control how (that is, through what function calls or property accessors) it wants to obtain the content.

Answer 1

There are more mechanisms than PHP string literal syntax to replace placeholders in strings! A pretty common one is sprintf:

$str = 'This is a %s';
$a   = 'test';
echo sprintf($str, $a);

http://php.net/sprintf

There are a ton of other more or less specialised templating languages. Pick the one you like best.

Answer 2

Have you heard of strtr()?

It serves this very purpose and is very useful to create dynamic HTML content containing information from a database, for example.

Given the following string:

$str = 'here is some text to greet user {zUserName}';

then you can parse it using strtr():

$userName = 'Mike';
$parsed = strtr($str,array('{zUserName}'=>$userName));
echo $parsed; // outputs: 'here is some text to greet user Mike'

While sprintf is faster in some regards, strtr allows you to control what goes where in a more friendly way (sprintf is not really manageable on very long strings containing, say, a hundred placeholders to be replaced).