Turn text between tags into a variable

[Michael S.]

How do I get the text between tags into a variable?

For example:

This is just [tag]a[/tag] test text!

I want to get: $variable = a;

[Smethead]

to use it in a function? do this:

//Open functions_post.php
//Find:
	$message = preg_replace("#\[email=(.*?)\](.*?)\[/email\]#i", "<a href=\"mailto:$1\">$2</a>", $message);
//After it, add:
	$message = preg_replace("#\[your_tag\](.*?)\[/your_tag\]#ei", "your_function(\"$1\")", $message);

$1 will be the text between the tags.

[Michael S.]

Thanks a lot!