Replace all characters in string apart from PHP

I have a string Trade Card Catalogue 1988 Edition I wish to remove everything apart from 1988.

I could have an array of all letters and do a str开发者_开发技巧_replace and trim, but I wondered if this was a better solution?

$string = 'Trade Card Catalogue 1988 Edition';
$letters = array('a','b','c'....'x','y','z');
$string = str_to_lower($string);
$string = str_replace($letters, '', $string);
$string = trim($string);

Thanks in advance

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Regular expression?

So assuming you want the number (and not the 4th word or something like that):

$str = preg_replace('#\D#', '', $str);

\D means every character that is not a digit. The same as [^0-9].

If there could be more numbers but you only want to get a four digit number (a year), this will also work (but obviously fails if you there are several four digit numbers and you want to get a specific one) :

$str = preg_replace('#.*?(\d{4,4}).*#', '\1', $str);

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You can actually just pass the entire set of characters to be trimmed as a parameter to trim:

$string = trim($string, 'abc...zABC...Z ' /* don't forget the space */);