addslashes
A use case of addslashes() is escaping the aforementioned characters in a string that is to be evaluated by PHP:
The addslashes() is sometimes incorrectly used to try to prevent SQL Injection. Instead, database-specific escaping functions and/or prepared statements should be used.
Parameters
Return Values
Returns the escaped string.
Examples
Example #1 An addslashes() example
// Outputs: Is your name O\’Reilly?
echo addslashes ( $str );
?>
See Also
- stripcslashes() — Un-quote string quoted with addcslashes
- stripslashes() — Un-quotes a quoted string
- addcslashes() — Quote string with slashes in a C style
- htmlspecialchars() — Convert special characters to HTML entities
- quotemeta() — Quote meta characters
- get_magic_quotes_gpc() — Gets the current configuration setting of magic_quotes_gpc
User Contributed Notes 19 notes
Never use addslashes function to escape values you are going to send to mysql. use mysql_real_escape_string or pg_escape at least if you are not using prepared queries yet.
keep in mind that single quote is not the only special character that can break your sql query. and quotes are the only thing which addslashes care.
To output a PHP variable to Javascript, use json_encode().
$var = «He said \»Hello O’Reilly\» & disappeared.\nNext line. » ;
echo «alert(» . json_encode ( $var ). «);\n» ;
Beware of using addslashes() on input to the serialize() function. serialize() stores strings with their length; the length must match the stored string or unserialize() will fail.
Such a mismatch can occur if you serialize the result of addslashes() and store it in a database; some databases (definitely including PostgreSQL) automagically strip backslashes from «special» chars in SELECT results, causing the returned string to be shorter than it was when it was serialized.
$string = «O’Reilly» ;
$ser = serialize ( $string ); # safe — won’t count the slash
$result = addslashes ( $ser );
?>
. and not this.
$string = «O’Reilly» ;
$add = addslashes ( $string ); # RISKY! — will count the slash
$result = serialize ( $add );
?>
In both cases, a backslash will be added after the apostrophe in «O’Reilly»; only in the second case will the backslash be included in the string length as recorded by serialize().
[Note to the maintainers: You may, at your option, want to link this note to serialize() as well as to addslashes(). I’ll refrain from doing such cross-posting myself. ]Remember to slash underscores (_) and percent signs (%), too, if you’re going use the LIKE operator on the variable or you’ll get some unexpected results.
addslashes does NOT make your input safe for use in a database query! It only escapes according to what PHP defines, not what your database driver defines. Any use of this function to escape strings for use in a database is likely an error — mysql_real_escape_string, pg_escape_string, etc, should be used depending on your underlying database as each database has different escaping requirements. In particular, MySQL wants \n, \r and \x1a escaped which addslashes does NOT do. Therefore relying on addslashes is not a good idea at all and may make your code vulnerable to security risks. I really don’t see what this function is supposed to do.
For PHP 7.3.* use FILTER_SANITIZE_ADD_SLASHES.
$str = «Is your name O’Reilly?» ;
$strWithSlashes = filter_var ( $str , FILTER_SANITIZE_ADD_SLASHES );
// Outputs: Is your name O\’Reilly?
echo $strWithSlashes ;
If all you want to do is quote a string as you would normally do in PHP (for example, when returning an Ajax result, inside a json string value, or when building a URL with args), don’t use addslashes (you don’t want both » and ‘ escaped at the same time). Instead, just use this function:
function Quote ( $Str ) // Double-quoting only
$Str = str_replace ( ‘»‘ , ‘\»‘ , $Str );
return ‘»‘ . $Str . ‘»‘ ;
> // Quote
?>
Modify this easily to get a single-quoting function.
This function is deprecated in PHP 4.0, according to this article:
Also, it is worth mentioning that PostgreSQL will soon start to block queries involving escaped single quotes using \ as the escape character, for some cases, which depends on the string’s encoding. The standard way to escape quotes in SQL (not all SQL databases, mind you) is by changing single quotes into two single quotes (e.g, ‘ ‘ ‘ becomes ‘ » ‘ for queries).
You should look into other ways for escaping strings, such as «mysql_real_escape_string» (see the comment below), and other such database specific escape functions.
Be careful on whether you use double or single quotes when creating the string to be escaped:
$test = ‘This is one line\r\nand this is another\r\nand this line has\ta tab’;
echo $test;
echo «\r\n\r\n»;
echo addslashes($test);
$test = «This is one line\r\nand this is another\r\nand this line has\ta tab»;
echo $test;
echo «\r\n\r\n»;
echo addslashes($test);
Addslashes is *never* the right answer, it’s (ab)use can lead to security exploits!
if you need to escape HTML, it’s (unfortunately)
echo htmlentities ( $html , ENT_QUOTES | ENT_SUBSTITUTE | ENT_DISALLOWED );
?>
if you need to quote shell arguments, it’s
$cmd .= » —file keyword»>. escapeshellarg ( $arg );
?>
if you need to quote SQL strings it’s
$sql .= «WHERE col = ‘» . $mysqli -> real_escape_string ( $str ). «‘» ;
?>
or
$sql .= «WHERE col keyword»>. $pdo -> quote ( $str );
?>
if you need to quote javascript/json strings its
let str = ;
?>
if you need to quote a string in xpath it’s
//based on https://stackoverflow.com/a/1352556/1067003
function xpath_quote ( string $value ): string if( false === strpos ( $value , ‘»‘ )) return ‘»‘ . $value . ‘»‘ ;
>
if( false === strpos ( $value , ‘\» )) return ‘\» . $value . ‘\» ;
>
// if the value contains both single and double quotes, construct an
// expression that concatenates all non-double-quote substrings with
// the quotes, e.g.:
//
// concat(«‘foo'», ‘»‘, «bar»)
$sb = ‘concat(‘ ;
$substrings = explode ( ‘»‘ , $value );
for( $i = 0 ; $i < count ( $substrings );++ $i )$needComma =( $i > 0 );
if( $substrings [ $i ]!== » ) if( $i > 0 ) $sb .= ‘, ‘ ;
>
$sb .= ‘»‘ . $substrings [ $i ]. ‘»‘ ;
$needComma = true ;
>
if( $i < ( count ( $substrings ) - 1 ))if( $needComma ) $sb .= ', ' ;
>
$sb .= «‘\»‘» ;
>
>
$sb .= ‘)’ ;
return $sb ;
>
$xp -> query ( ‘/catalog/items/item[title=’ . xpath_quote ( $var ). ‘]’ );
?>
if you need to quote strings in CSS its
// CSS escape code ripped from Zend Framework ( https://github.com/zendframework/zf2/blob/master/library/Zend/Escaper/Escaper.php )
function css_escape_string ( $string )
$cssMatcher = function ( $matches ) $chr = $matches [ 0 ];
if ( strlen ( $chr ) == 1 ) $ord = ord ( $chr );
> else $chr = mb_convert_encoding ( $chr , ‘UTF-16BE’ , ‘UTF-8’ ); // $this->convertEncoding($chr, ‘UTF-16BE’, ‘UTF-8’);
$ord = hexdec ( bin2hex ( $chr ));
>
return sprintf ( ‘\\%X ‘ , $ord );
>;
$originalEncoding = mb_detect_encoding ( $string );
if ( $originalEncoding === false ) $originalEncoding = ‘UTF-8’ ;
>
;
$string = mb_convert_encoding ( $string , ‘UTF-8’ , $originalEncoding ); // $this->toUtf8($string);
// throw new Exception(‘mb_convert_encoding(\».$string.’\’,\’UTF-8\’,\».$originalEncoding.’\’);’);
if ( $string === » || ctype_digit ( $string )) return $string ;
>
$result = preg_replace_callback ( ‘/[^a-z0-9]/iSu’ , /*$this->*/ $cssMatcher , $string );
// var_dump($result);
return mb_convert_encoding ( $result , $originalEncoding , ‘UTF-8’ ); // $this->fromUtf8($result);
>
Note that when using addslashes() on a string that includes cyrillic characters, addslashes() totally mixes up the string, rendering it unusable.
spamdunk at home dot com, your way is dangerous on PostgreSQL (and presumably MySQL). You’re quite correct that ANSI SQL specifies using ‘ to escape, but those databases also support \ for escaping (in violation of the standard, I think). Which means that if they pass in a string that includes a «\'», you expand it to «\»'» (an escaped quote followed by a non-escaped quote. WRONG! Attackers can execute arbitrary SQL to drop your tables, make themselves administrators, whatever they want.)
The best way to be safe and correct is to:
— don’t use magic quotes; this approach is bad. For starters, that’s making the assumption that you will be using your input in a database query, which is arbitrary. (Why not escape all »
— when inserting into the database, use prepared statements with placeholders. For example, when using PEAR DB:
$stmt = $dbh -> prepare ( ‘update mb_users set password = ? where username = ?’ );
$dbh -> execute ( $stmt , array( ‘12345’ , ‘bob’ ));
?>
Notice that there are no quotes around the ?s. It handles that for you automatically. It’s guaranteed to be safe for your database. (Just ‘ on oracle, \ and ‘ on PostgreSQL, but you don’t even have to think about it.)
Plus, if the database supports prepared statements (the soon-to-be-released PostgreSQL 7.3, Oracle, etc), several executes on the same prepare can be faster, since it can reuse the same query plan. If it doesn’t (MySQL, etc), this way falls back to quoting code that’s specifically written for your database, avoiding the problem I mentioned above.
(Pardon my syntax if it’s off. I’m not really a PHP programmer; this is something I know from similar things in Java, Perl, PL/SQL, Python, Visual Basic, etc.)