不输出正则表达式中的捕获组

Question

<?php
    $string = 'This is my regular expression';
    $array = array();
    preg_match('/^.*((my)? regular (expression)?)$/i', $string, $array);
    var_dump($array);
?>

After execution of this script I have:

array (size=4)
    0 => string 'This is my regular expression' (length=29)
    1 => string ' regular expression' (length=19)
    2 => string '' (length=0)
    3 => string 'expression' (length=10)

Why it doesn't output capturing group (my)?

Answer 1

That is because you have a greedy quantifier .* before it. You should instead use a non greedy quantifier .*? .

Do it as follows instead:

<?php
    $string = 'This is my regular expression';
    $array = array();
    preg_match('/^.*?((my)? regular (expression)?)$/i', $string, $array);
    var_dump($array);
?>

DEMO

[OUTPUT]

array (size=4)
0 => string 'This is my regular expression' (length=29)
1 => string 'my regular expression' (length=21)
2 => string 'my' (length=2)
3 => string 'expression' (length=10)