Regex to get first number in string with other characters

Question

I\'m new to regular expressions, and was wondering how I could get only the first number in a string like 100 2011-10-20 14:28:55. In this case, I\'d want it to

Answer 1

Assuming there's always a space between the first two numbers, then

preg_match('/^(\d+)/', $number_string, $matches);
$number = $matches[1]; // 100

But for something like this, you'd be better off using simple string operations:

$space_pos = strpos($number_string, ' ');
$number = substr($number_string, 0, $space_pos);

Regexs are computationally expensive, and should be avoided if possible.