$re = '/["\'`][^"\'`]*(?!\\\\)["\'`](*SKIP)(*F) # Make sure we\'re not matching inside of quotes, double quotes or backticks
|(?m-s:\s*(?:\-{2}|\#)[^\n]*$) # Single line comment
|(?:
\/\*.*?\*\/ # Multi-line comment
(?(?=(?m-s:[\t ]+$)) # Get trailing whitespace if any exists and only if it\'s the rest of the line
[\t ]+
)
)/xs';
$str = 'SELECT `#comment inside string`;';
$subst = "";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php