(PHP 4, PHP 5, PHP 7)
preg_quote — Quote regular expression characters
$str
  [, string $delimiter = NULL
  ] )
   preg_quote() takes str
   and puts a backslash in front of every character that is part of
   the regular expression syntax.  This is useful if you have a
   run-time string that you need to match in some text and the
   string may contain special regex characters.
  
The special regular expression characters are: . \ + * ? [ ^ ] $ ( ) { } = ! < > | : -
strThe input string.
delimiter
       If the optional delimiter is specified, it
       will also be escaped.  This is useful for escaping the delimiter
       that is required by the PCRE functions. The / is the most commonly
       used delimiter.
      
Returns the quoted (escaped) string.
| Version | Description | 
|---|---|
| 5.3.0 | The - character is now quoted | 
Example #1 preg_quote() example
<?php
$keywords = '$40 for a g3/400';
$keywords = preg_quote($keywords, '/');
echo $keywords; // returns \$40 for a g3\/400
?>
Example #2 Italicizing a word within some text
<?php
// In this example, preg_quote($word) is used to keep the
// asterisks from having special meaning to the regular
// expression.
$textbody = "This book is *very* difficult to find.";
$word = "*very*";
$textbody = preg_replace ("/" . preg_quote($word, '/') . "/",
                          "<i>" . $word . "</i>",
                          $textbody);
?>
Note: This function is binary-safe.