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In PHP, mb_eregi_replace is a regular expression replacement function designed for multibyte strings, with case-insensitive matching. It follows POSIX regular expression syntax, which means it does not support named groups like PCRE (preg_* functions). Named groups allow certain parts of a regular expression to have meaningful names, making the code easier to maintain and read.
This article will explain how, although mb_eregi_replace does not natively support named groups, you can simulate their effect through workarounds.
The regular expression syntax used by mb_eregi_replace does not support PCRE-style named groups, such as (?
Example:
$pattern = '([a-z]+)'; // Regular group
But you cannot write it as:
$pattern = '(?<word>[a-z]+)'; // Named groups are not supported
Therefore, to reference a group, you must use numeric indexes, such as \1, \2, etc.
Although mb_eregi_replace cannot directly use named groups, we can combine regular groups with a callback function during replacement to simulate the effect.
However, mb_eregi_replace itself does not have a callback version. We can first use the mb_ereg_search series of functions for matching, capture the group contents, and then implement the replacement logic in PHP.
Example process:
Use mb_ereg_search_init and mb_ereg_search to match the string step-by-step.
After each match, get the group contents and perform manual replacements.
Use PHP arrays to simulate the structure of named groups.
The following code demonstrates how to use the mb_ereg_search series of functions to capture group contents, simulate named groups, and perform replacements:
<?php
<p>// The string to process<br>
$text = "User: alice, Email: <a class="cursor-pointer" rel="noopener">alice@example.com</a>";</p>
<p>// POSIX-style regex with two groups: username and email<br>
$pattern = 'User: ([a-z]+), Email: ([a-z0-9._%-]+@[a-z0-9.-]+.[a-z]{2,})';</p>
<p>// Initialize search<br>
mb_ereg_search_init($text, $pattern, 'i'); // i stands for case-insensitive matching</p>
<p>$result = '';<br>
$offset = 0;</p>
<p>while ($match = mb_ereg_search_pos()) {<br>
// Get the match start position and length<br>
list($start, $length) = $match;</p>
$fullMatch = mb_substr($text, $start, $length);
// Get the captured group contents
$regs = mb_ereg_search_getregs();
// Simulate named groups
$namedGroups = [
'username' => $regs[1],
'email' => $regs[2],
];
// Process replacement logic, e.g., capitalize the username, mask part of the email
$replacement = "User: " . strtoupper($namedGroups['username']) . ", Email: " . maskEmail($namedGroups['email']);
// Concatenate the result
$result .= mb_substr($text, $offset, $start - $offset) . $replacement;
$offset = $start + $length;
// Continue searching
mb_ereg_search_setpos($offset);
}
// Concatenate the remaining part
$result .= mb_substr($text, $offset);
echo $result;
// Helper function to mask part of the email
function maskEmail($email) {
$parts = explode('@', $email);
$name = $parts[0];
$domain = $parts[1];
$maskedName = substr($name, 0, 1) . str_repeat('*', max(0, strlen($name) - 2)) . substr($name, -1);
return $maskedName . '@' . $domain;
}
?>
Since mb_eregi_replace does not support callbacks directly, we use mb_ereg_search_init and related functions to perform looped matching and manually handle replacements.
We capture group contents using the $regs array and simulate named groups by using array keys, making the code clearer.
The replacement process is fully handled in PHP code, allowing for any complex logic to be applied.
The example includes logic to capitalize the username and mask part of the email address.
Although the mb_eregi_replace function itself does not support named groups, by using the mb_ereg_search series of functions along with PHP code, we can simulate named groups, improving the readability and maintainability of the code.
If you need more complex regular expression features and native support for named groups, it is recommended to use preg_replace_callback, but note that it does not support multibyte encoding as well as the mb_ereg series.
