preg_match() - Regular Expression Match

PHP Modules Tutorials - Herong's Tutorial Examples

∟PCRE Module - Perl Compatible Regular Expressions

∟preg_match() - Regular Expression Match

This section provides a tutorial example on how to search for the first occurrence and all occurrences with a given regular expression pattern using preg_match() and preg_match_all() functions.

The most commonly used regular expression operation is the pattern match operation. PCRE module provides 2 pattern match functions:

$found = preg_match($pattern, $subject, $matches, $flags);
$found = preg_match_all($pattern, $subject, $matches, $flags);

where: 
  $pattern: The regular express pattern to search for
  $subject: The string to search against
  $matches: Array to store matched substrings
  $flags: Optional - Binary flags to turn various options
    PREG_OFFSET_CAPTURE: Flag to capture offsets of matches
    PREG_SET_ORDER: Flag to order matches by occurrence
  $found: Boolean true if match found

Here is an example script that searches regular expression patterns for the first occurrence and all occurrences.

<?php
# preg-match-with-sub-pattern.php
# Copyright 2009-2024 (c) HerongYang.com. All Rights Reserved.

  $subject = "herongyang.com/PHP, herongyang.com/Python";
  $pattern = "/[^\/]+\/([^,]+)/";
  print("Subject: $subject\n");
  print("Pattern: $pattern\n");

  print("Match for the first occurrence:\n");
  $flags = 0;
  $found = preg_match($pattern, $subject, $matches, $flags);
  if ($found) {
    print("  First match: {$matches[0]}\n");
    print("  First sub-match: {$matches[1]}\n");
  } else {
    print("  No match found\n");
  }

  print("Match for the first occurrence and return offsets:\n");
  $flags = PREG_OFFSET_CAPTURE;
  $found = preg_match($pattern, $subject, $matches, $flags);
  if ($found) {
    print("  First match: {$matches[0][0]} at {$matches[0][1]}\n");
    print("  First sub-match: {$matches[1][0]} at {$matches[1][1]}\n");
  } else {
    print("  No match found\n");
  }

  print("Match for all occurrences:\n");
  $flags = PREG_SET_ORDER;
  $found = preg_match_all($pattern, $subject, $matches, $flags);
  if ($found) {
    for ($i=0; $i<count($matches); $i++) {
      print("  Match #".($i+1).":\n");
      print("    Full match: {$matches[$i][0]}\n");
      print("    Sub-match: {$matches[$i][1]}\n");
    }
  } else {
    print("  No match found\n");
  }
?>

If you run the above script, you will see the following output:

herong$ preg-match-with-sub-pattern.php 

Subject: herongyang.com/PHP, herongyang.com/Python
Pattern: /[^\/]+\/([^,]+)/

Match for the first occurrence:
  First match: herongyang.com/PHP
  First sub-match: PHP

Match for the first occurrence and return offsets:
  First match: herongyang.com/PHP at 0
  First sub-match: PHP at 15

Match for all occurrences:
  Match #1:
    Full match: herongyang.com/PHP
    Sub-match: PHP
  Match #2:
    Full match: , herongyang.com/Python
    Sub-match: Python