3v4l.org

run code in 300+ PHP versions simultaneously
<?php echo preg_replace_callback('~[A-Z]~', function($_) { return $_ + 32; }, 'Important: you are NOT allowed to use a built-in function that converts the string (or just one character) to lowercase (such as ToLower() in .NET, strtolower() in PHP , ...)! You're allowed to use all other built-in functions, however.')
Output for 5.4.0 - 5.4.20
Parse error: syntax error, unexpected 're' (T_STRING) in /in/bCd7U on line 2
Process exited with code 255.
Output for 5.3.0 - 5.3.27
Parse error: syntax error, unexpected T_STRING in /in/bCd7U on line 2
Process exited with code 255.
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179.14 ms | 1395 KiB | 56 Q