Script to demonstrate the PCRE ability to define subpattern.

pcre-define-test.php

<?php

$testString = '192.168.0.1';
$regex1 = trim('
^                     # Matches begin of string
(
  \d|                 # Matches either a single digit or
  [1-9]\d|            # a number between 10 and 99 or
  1\d\d|              # a number between 100 and 199 or
  2[0-4]\d|           # a number between 200 and 249 or
  25[0-5]             # a number between 250 and 255
)
(
  \.                  # Matches the dot character literally "."
  (
    \d|               # Matches either a single digit or
    [1-9]\d|          # a number between 10 and 99 or
    1\d\d|            # a number between 100 and 199 or
    2[0-4]\d|         # a number between 200 and 249 or
    25[0-5]           # a number between 250 and 255
  )
)
{3}                   # Matches the previous group exactly three times
$                     # Matches end of string
');

$regex2 = trim('
(?(DEFINE)(?<bg>25[0-5]|2[0-4]\d|1\d\d|[1-9]\d|\d)) # Defines a bytegroup
^              # Matches begin of string
(?&bg)         # References a bytegroup
(
  \.           # Matches the dot literally "."
  (?&bg)       # References a bytegroup
)     
{3}            # Matches the previous group exactly three times
$              # Matches end of string
');

$regex3 = trim('
(?(DEFINE)(?<byteg>25[0-5]|2[0-4]\d|1\d\d|[1-9]\d|\d)) # Defines a bytegroup
(?(DEFINE)(?<dot>\.)) # Defines the dot literally

^(?&byteg)(?&dot)(?&byteg)(?&dot)(?&byteg)(?&dot)(?&byteg)$
');


echo "Test: $testString" . PHP_EOL;
echo "Regex:" . PHP_EOL . $regex1 . PHP_EOL;
echo "Result: " . preg_match("/$regex1/x", $testString, $matches) . PHP_EOL;
echo "Matches: "; print_r($matches);
echo PHP_EOL;
echo "Test: $testString" . PHP_EOL;
echo "Regex:" . PHP_EOL . $regex2 . PHP_EOL;
echo "Result: " . preg_match("/$regex2/x", $testString, $matches) . PHP_EOL;
echo "Matches: "; print_r($matches);
echo PHP_EOL;
echo "Test: $testString" . PHP_EOL;
echo "Regex:" . PHP_EOL . $regex3 . PHP_EOL;
echo "Result: " . preg_match("/$regex3/x", $testString, $matches) . PHP_EOL;
echo "Matches: "; print_r($matches);
echo PHP_EOL;