preg_replace() - Replace Matched Substring

PHP Modules Tutorials - Herong's Tutorial Examples

∟PCRE Module - Perl Compatible Regular Expressions

∟preg_replace() - Replace Matched Substring

This section provides a tutorial example on how to search and replace regular expression patterns using preg_replace() and preg_match_filter() functions.

If you want to search and replace substrings, you can you can use the preg_replace() or preg_filter() function:

$outputs = preg_replace($patterns, $replacements, $subjects);
$replaced = preg_filter($patterns, $replacements, $subjects);

where: 
  $patterns: Regular express pattern, or array of patterns, 
    which are searched and replaced sequentially
  $replacements: Replacement, or array of replacements, 
     which may contain $n or /n to refer to matches
  $subjects: Subject, or array of subjects 
  $outputs: Subject, or array of subject after replacements
  $replaced: Subjects that are affected by replacements

Here is an example script that searches and replaces expression patterns in a given string or array of strings.

<?php 
# preg-replace-and-filter.php
# Copyright 2009-2024 (c) HerongYang.com. All Rights Reserved.

  print("Test 1 - String arguments:\n");
  $subject = "The quick brown fox jumps over the lazy dog";
  $pattern = "/(fox)(.*)(dog)/i";
  $replacement = "$3$2$1";
  pcre_test($pattern, $replacement, $subject); 

  print("Test 2 - String Array arguments:\n");
  $subjects = array(
    "The quick brown fox jumps over the lazy dog",
    "The quick brown cat jumps over the lazy dog",
    "The quick black cat jumps over the fast dog"
  );
  $patterns = array(
    "/(fox)(.*)(dog)/i",
    "/brown/i",
    "/lazy/i",
  );
  $replacements = array(
    "$3$2$1",
    "lazy",
    "red",
  );
  pcre_test($patterns, $replacements, $subjects); 

function pcre_test($patterns, $replacements, $subjects) {
  print("  Patterns:\n"
    .json_encode($patterns, JSON_PRETTY_PRINT)."\n");
  print("  Replacements:\n"
    .json_encode($replacements, JSON_PRETTY_PRINT)."\n");
  print("  Original subjects:\n"
    .json_encode($subjects, JSON_PRETTY_PRINT)."\n");

  $outputs = preg_replace($patterns, $replacements, $subjects);
  print("  Replaced subjects - affected and non-affected:\n"
    .json_encode($outputs, JSON_PRETTY_PRINT)."\n");

  $replaced = preg_filter($patterns, $replacements, $subjects);
  print("  Replaced subjects - affected only:\n"
    .json_encode($replaced, JSON_PRETTY_PRINT)."\n");
}
?>

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

herong$ php preg-replace-and-filter.php

Test 1 - String arguments:
  Patterns:
"\/(fox)(.*)(dog)\/i"
  Replacements:
"$3$2$1"
  Original subjects:
"The quick brown fox jumps over the lazy dog"
  Replaced subjects - affected and non-affected:
"The quick brown dog jumps over the lazy fox"
  Replaced subjects - affected only:
"The quick brown dog jumps over the lazy fox"

Test 2 - String array arguments:
  Patterns:
[
    "\/(fox)(.*)(dog)\/i",
    "\/brown\/i",
    "\/lazy\/i"
]
  Replacements:
[
    "$3$2$1",
    "lazy",
    "red"
]
  Original subjects:
[
    "The quick brown fox jumps over the lazy dog",
    "The quick brown cat jumps over the lazy dog",
    "The quick black cat jumps over the fast dog"
]
  Replaced subjects - affected and non-affected:
[
    "The quick red dog jumps over the red fox",
    "The quick red cat jumps over the red dog",
    "The quick black cat jumps over the fast dog"
]
  Replaced subjects - affected only:
[
    "The quick red dog jumps over the red fox",
    "The quick red cat jumps over the red dog"
]

Note that:

If the first argument is array of patterns, all of them will be applied to each subject sequentially.
Each pattern is applied globally for all occurrences.