How can conditional statements be incorporated into regular expressions in PHP, and what are common pitfalls to avoid?

Conditional statements can be incorporated into regular expressions in PHP using the `(?ifthen|else)` syntax. This allows you to define patterns that include conditions to match specific cases. Common pitfalls to avoid include ensuring proper syntax for the conditional statements, escaping special characters within the regular expression, and testing the regular expression thoroughly to account for all possible cases. 

$pattern = '/^(?:(?P<digit>\d+)|(?P<word>\w+))$/';

$input = '123';
if (preg_match($pattern, $input, $matches)) {
    if (!empty($matches['digit'])) {
        echo 'Matched digits: ' . $matches['digit'];
    } elseif (!empty($matches['word'])) {
        echo 'Matched word: ' . $matches['word'];
    }
} else {
    echo 'No match found.';
}

Keywords

PHP regular expressions conditional statements pitfalls syntax

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