PHP带标点符号。

# to keep letters & numbers
$s = preg_replace(\'/[^a-z0-9]+/i\', \'_\', $s); # or...
$s = preg_replace(\'/[^a-z\\d]+/i\', \'_\', $s);

# to keep letters only
$s = preg_replace(\'/[^a-z]+/i\', \'_\', $s); 

# to keep letters, numbers & underscore
$s = preg_replace(\'/[^\\w]+/\', \'_\', $s);

# same as third example; suggested by @tchrist; ^\\w = \\W
$s = preg_replace(\'/\\W+/\', \'_\', $s);

$s = \"Hello, is StackOverflow a helpful website!? Yes!\";

function strip_punctuation($string) {
    $string = strtolower($string);
    $string = preg_replace(\"/[:punct:]+/\", \"\", $string);
    $string = str_replace(\" +\", \"_\", $string);
    return $string;
}

<?php
  $hello = \"Hello, is StackOverflow a helpful website!? Yes!\"; // original string
  $unwantedChars = array(\',\', \'!\', \'?\'); // create array with unwanted chars
  $hello = str_replace($unwantedChars, \'\', $hello); // remove them
  $hello = strtolower($hello); // convert to lowercase
  $hello = str_replace(\' \', \'_\', $hello); // replace spaces with underline
  echo $hello; // outputs: hello_is_stackoverflow_a_helpful_website_yes
?>

$str = preg_replace(\'/[^\\w\\s]/\', \'\', $str);

$str = preg_replace(\'/\\s+/\', \'_\', $str);