Clever Geek Handbook

How to improve the readability of regular expressions in PHP

Regular expressions are a very powerful tool, but the conventional wisdom is that once they are written, they are very difficult to understand, so maintaining them is not a pleasant experience. Collected here are tips to help make them more readable.





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preg_match('/^https:\/\/example.com\/path/i', $uri);

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preg_match('#^https://example.com/path#i', $uri);

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/Price: [0-9\-\$\.\+]+/
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    





/Price: [0-9$.+-]+/

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preg_match('/x\yz/X', ''); //  "y" β€” ,   β€”

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Warning: preg_match(): Compilation failed: unrecognized character follows \ at offset 2 in ... on line ...

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$pattern = '/Price: (Β£|€)(\d+)/';
$text    = 'Price: €24';
preg_match($pattern, $text, $matches);

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var_dump($matches);

array(3) {
  [0]=> string(12) "Price: €24"
  [1]=> string(3) "€"
  [2]=> string(2) "24"
}

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$pattern = '/Price: (?:Β£|€)(\d+)/';
$text    = 'Price: €24';
preg_match($pattern, $text, $matches);
var_dump($matches);

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array(2) {
  [0]=> string(12) "Price: €24"
  [1]=> string(2) "24"
}

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/Price: (?<currency>Β£|€)(?<price>\d+)/

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$pattern = '/Price: (?<currency>Β£|€)(?<price>\d+)/';
$text    = 'Price: €24';
preg_match($pattern, $text, $matches);
var_dump($matches);

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array(5) {
 [0]=> string(12) "Price: €24"
["currency"]=> string(3) "€"
[1]=> string(3) "€"
["price"]=> string(2) "24"
[2]=> string(2) "24"
}

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Warning: preg_match(): Compilation failed: two named subpatterns have the same name (PCRE2_DUPNAMES not set) at offset ... in ... on line ....

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/Price: (?<currency>Β£|€)?(?<price>\d+)(?<currency>Β£|€)?/J

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$pattern = '/Price: (?<currency>Β£|€)?(?<price>\d+)(?<currency>Β£|€)?/J';
$text    = 'Price: €24Β£';
preg_match($pattern, $text, $matches);
var_dump($matches);

array(6) {
  [0]=> string(14) "Price: €24Β£"
  ["currency"]=> string(2) "Β£"
  [1]=> string(3) "€"
  ["price"]=> string(2) "24"
  [2]=> string(2) "24"
  [3]=> string(2) "Β£"
}

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$pattern  = '/Price: (?<currency>Β£|€)(?<price>\d+)/i';

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$pattern  = '/Price: ';
$pattern .= '(?<currency>Β£|€)'; // Capture currency symbols Β£ or €
$pattern .= '(?<price>\d+)'; // Capture price without decimals.
$pattern .= '/i'; // Flags: Case-insensitive

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/Price: (?<currency>Β£|€)(?<price>\d+)/i
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    





/Price:  \s  (?<currency>Β£|€)  (?<price>\d+)  /ix

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/Price: (?<currency>Β£|€)(?<price>\d+)/i

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/Price:           # Check for the label "Price:"
\s                # Ensure a white-space after.
(?<currency>Β£|€)  # Capture currency symbols Β£ or €
(?<price>\d+)     # Capture price without decimals.
/ix

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$pattern = <<<PATTERN
  /Price:           # Check for the label "Price:"
  \s                # Ensure a white-space after.
  (?<currency>Β£|€)  # Capture currency symbols Β£ or €
  (?<price>\d+)     # Capture price without decimals.
  /ix               # Flags: Case-insensitive
PATTERN;

preg_match($pattern, 'Price: Β£42', $matches);

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$pattern = '/Price: \p{Sc}\d+/u';

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$text = 'Price: Β₯42';

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$pattern = '/[\x{0D80}-\x{0DFF}]/u';

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$pattern = '/\p{Sinhala}/u';

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$text = 'ΰΆ΄ΰ·“ΰΆ‘ΰΆ ΰ·ŠΰΆ΄ΰ·“.ΰ·€ΰ·œΰΆ ΰ·Š`;
$contains_sinhala = preg_match($pattern, $text);

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