preg_match问题

I'm trying to use preg_match to find php code statements in template files so I can convert them to a different syntax (smarty).

Executing the following example isn't producing any matches, can someone let me know what I'm doing wrong?

$test = '<?=$test?>';
preg_match( '/<?=$([a-z]+)?>/', $test, $code );

preg_match( '/<\?=\$([a-z]+)\?>/i', $test, $code );

Also you can safely omit the parenthesis there

preg_match( '/<\?=\$[a-z]+\?>/i', $test, $code );

You have to escape special chars, that are used in regular expressions. You can use preg_quote() for this purpose