preg_replace和file_get_contents - 如何获得$ {1}？

Question

I have this piece of code:

echo preg_replace('/\!(.*)\!/', file_get_contents('${1}'), $str);

What it is meant to do is replacing all !...! with the contents of the file specified between the exclamation marks. However, it is not working because ${1} is not getting replaced:

Warning: file_get_contents(${1}) [function.file-get-contents]: failed to open stream: No such file or directory

If I code:

echo preg_replace('/\!(.*)\!/', '${1}', $te);

everything is fine (i.e. the text between !...! is replaced by the text itself).

How can I make the ${1} in file_get_contents also be replaced?

Answer 1

echo preg_replace_callback('/\!(.*)\!/', function($matches) {
    return file_get_contents($matches[1]);
}, $str);

There you go. Use preg_replace_callback for this kind of replacements, where you need to call a custom function on the matches that would give the replacement string.