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How to Replace Variable Names in PHP Files Using mb_eregi_replace (Use with Caution, May Affect Global Scope)

M66 2025-06-23

In PHP, if you need to replace variable names in a file, you can usually use regular expression functions to achieve this. mb_eregi_replace is a multibyte-safe regular expression replacement function that supports case-insensitive matching, making it suitable for handling content containing multibyte characters (such as Chinese).

However, when using mb_eregi_replace to replace variable names, special care must be taken because it is a global replacement based on regular expressions. This can potentially affect part of a variable name or other similar strings, causing errors in your program.

The following example demonstrates how to use mb_eregi_replace to replace variable names in a PHP file.

<?php
// Assume we have a PHP file content stored in the string $code
$code = <<<'PHP'
<?php
$oldVar = 123;
echo $oldVar;
$oldVariable = 456;
?>
PHP;
<p>// The goal is to replace all instances of the variable $oldVar with $newVar,<br>
// Be careful not to mistakenly replace $oldVariable, which contains the old variable name.</p>
<p>// Use mb_eregi_replace to replace the variable name, with a regular expression matching $oldVar as the exact variable name<br>
// Use the word boundary \b to prevent partial matches, and note that the $ symbol in PHP needs to be escaped<br>
$pattern = '/\boldVar\b/i'; // Case-insensitive match for the variable name oldVar<br>
$replacement = 'newVar';</p>
<p>// Perform the replacement<br>
// Note: Here, only the variable name part is replaced, excluding the $ symbol because it is not included in the regex<br>
// If you need to replace variables with the $ symbol, the regex should be modified to '/$oldVar\b/i'<br>
$pattern = '/$oldVar\b/i';<br>
$newCode = mb_eregi_replace($pattern, '$newVar', $code);</p>
<p>// Output the modified code<br>
echo $newCode;<br>
?><br>

Important Tips

  1. Ensure Accurate Matching Scope
    When replacing variable names, always use word boundaries (\b) to match full words and avoid replacing part of a variable name.

  2. Use Global Replacement with Caution
    mb_eregi_replace performs a global replacement, so if there are similar identifiers or strings in the file, they may be mistakenly replaced.

  3. Backup Files
    Always back up the original file before performing batch replacements to avoid irreversible errors.

  4. Debug Output
    You can first print the replacement results to confirm that everything is correct before writing it back to the file.

Using the method described above, you can replace specific variable names in PHP files with mb_eregi_replace, but always exercise caution to avoid unintended consequences in your code.

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