PHP：在字符串变量中交换占位符以获取相应的已定义变量值

Question

I have a PHP script with some variables set in the global namespace:

$domain = 'example.com';
$hostname = 'www.' . $domain;

I am reading an external file into a string variable in my script using file_get_contents:

$file_contents = file_get_contents('external_file.tpl');

The external file (and the string $file_contents) contains placeholders which correspond to variable names.

127.0.0.1 {{domain}} {{hostname}}

I would like to have all the placeholders in the variable $file_contents replaced with their respective PHP variables already set. I want this to work generically (without hard-coding placeholder / variable names). I do not want to edit the file, just the contents of the string.

What's the easiest way to do this?

Answer 1

Alright guys, I took some bits and pieces from other answers and came up with what I think is the best solution for me:

$domain = 'example.com';
$hostname = 'www.' . $domain;
$file_contents = '127.0.0.1 {{domain}} {{hostname}}';

$result = preg_replace_callback(
    "/{{(.+?)}}/",
    function ($matches) {
        return $GLOBALS[$matches[1]];
    },
    $file_contents
);

This answer combines ideas from @TonyDeStefano, @dops, and @fschmengler. So please up-vote them. @BugaDániel also helped with his comments.