Regular expression and trailing slash

I have this regular expression in PHP with the preg_match/preg_replace functions:

/test\/([A-Za-z]+)\/([A-Za-z]+)\/?([A-Za-z]+)?\/?/

=>

test/\1_\2/\3/

What I want is, that if it only says http://domain.com/test then it doesn't matter wheter there is a trailing slash or not - how do I do that?

EDIT:

I am doing this:

I have this array:

$routing = array(
    '/test\/([A-Za-z]+)\/([A-Za-z]+)\/?([A-Za-z]+)?\/?/' => 'test/\1_\2/\3/',

    '/error\/([0-9]+)/' =&g开发者_如何学编程t; 'error/error_\1',
    '/sitemap\.html/' => 'sitemap',
    '/search\/([^\/]+)?/' => 'search/view/$1',
);

What I do is, that I perform this action to route the URL:

global $routing;

foreach ( $routing as $pattern => $result ) {
    if ( preg_match( $pattern, $url ) ) {
        return preg_replace( $pattern, $result, $url );
    }
}

return ($url);

My framework is doing this in the routing:

E.g. the url can be test/stack/hello/21 which is = to Test::stack_hello(21)

So the set up is actually: controller/func/tion/parameter = function/func_tion/parameter.

$regex = '#test(?:/([a-z]+))(?:/([a-z]+))(?:/([a-z]+))/?$#i';

This matches a string that contains test, followed by a / and a series of letters, then that pattern is repeated twice more. The last character of the string to match is an optional / (and then the string should end because of the $). The pattern is repeated three times because that's the only way all three matches can be used as replacement patterns.

$text = 'test/abc/de/f';
$replacement = 'test/\1_/\3/\2/'; // de and f should switch places
var_dump(preg_replace($regex, $replacement, $text));

That shows the string test/abc_/f/de/