Check part of string is in_array()

[eluser]codex[/eluser]
Is it possible to check whether if only a part of a string is present in an array?

See, i need to check if 'min_length[8]' is in_array, but since the number is variable I can't check the whole string, so I just need to know if 'min_length' is found.

Also, I need to return the value between the brackets ([]). Is there a PHP function lets me get 'anything between char [ and char ]'? Or is this requiring regex stuff?