mysqli::real_escape_string

(PHP 5, PHP 7)

mysqli::real_escape_string -- mysqli_real_escape_string — Escapes special characters in a string for use in an SQL statement, taking into account the current charset of the connection

Description ¶

Object oriented style

string mysqli::escape_string ( string $escapestr )

string mysqli::real_escape_string ( string $escapestr )

Procedural style

string mysqli_real_escape_string ( mysqli $link , string $escapestr )

This function is used to create a legal SQL string that you can use in an SQL statement. The given string is encoded to an escaped SQL string, taking into account the current character set of the connection.

Caution

Security: the default character set

The character set must be set either at the server level, or with the API function mysqli_set_charset() for it to affect mysqli_real_escape_string(). See the concepts section on character sets for more information.

Parameters ¶

link

Procedural style only: A link identifier returned by mysqli_connect() or mysqli_init()

escapestr

The string to be escaped.

Characters encoded are NUL (ASCII 0), \n, \r, \, ', ", and Control-Z.

Return Values ¶

Returns an escaped string.

Errors/Exceptions ¶

Executing this function without a valid MySQLi connection passed in will return NULL and emit E_WARNING level errors.

Examples ¶

Example #1 mysqli::real_escape_string() example

Object oriented style

<?php
$mysqli = new mysqli("localhost", "my_user", "my_password", "world");

/* check connection */
if (mysqli_connect_errno()) {
    printf("Connect failed: %s\n", mysqli_connect_error());
    exit();
}

$mysqli->query("CREATE TEMPORARY TABLE myCity LIKE City");

$city = "'s Hertogenbosch";

/* this query will fail, cause we didn't escape $city */
if (!$mysqli->query("INSERT into myCity (Name) VALUES ('$city')")) {
    printf("Error: %s\n", $mysqli->sqlstate);
}

$city = $mysqli->real_escape_string($city);

/* this query with escaped $city will work */
if ($mysqli->query("INSERT into myCity (Name) VALUES ('$city')")) {
    printf("%d Row inserted.\n", $mysqli->affected_rows);
}

$mysqli->close();
?>

Procedural style

<?php
$link = mysqli_connect("localhost", "my_user", "my_password", "world");

/* check connection */
if (mysqli_connect_errno()) {
    printf("Connect failed: %s\n", mysqli_connect_error());
    exit();
}

mysqli_query($link, "CREATE TEMPORARY TABLE myCity LIKE City");

$city = "'s Hertogenbosch";

/* this query will fail, cause we didn't escape $city */
if (!mysqli_query($link, "INSERT into myCity (Name) VALUES ('$city')")) {
    printf("Error: %s\n", mysqli_sqlstate($link));
}

$city = mysqli_real_escape_string($link, $city);

/* this query with escaped $city will work */
if (mysqli_query($link, "INSERT into myCity (Name) VALUES ('$city')")) {
    printf("%d Row inserted.\n", mysqli_affected_rows($link));
}

mysqli_close($link);
?>

The above examples will output:

Error: 42000
1 Row inserted.

Notes ¶

Note:

For those accustomed to using mysql_real_escape_string(), note that the arguments of mysqli_real_escape_string() differ from what mysql_real_escape_string() expects. The link identifier comes first in mysqli_real_escape_string(), whereas the string to be escaped comes first in mysql_real_escape_string().

See Also ¶

• mysqli_set_charset() - Sets the default client character set
• mysqli_character_set_name() - Returns the default character set for the database connection

 add a note

User Contributed Notes 12 notes

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111

tobias_demuth at web dot de ¶

12 years ago

Note, that if no connection is open, mysqli_real_escape_string() will return an empty string!

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54

Josef Toman ¶

7 years ago

For percent sign and underscore I use this:
<?php
$more_escaped = addcslashes($escaped, '%_');
?>

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4

therselman at gmail dot com ¶

5 months ago

Presenting several UTF-8 / Multibyte-aware escape functions.

These functions represent alternatives to mysqli::real_escape_string, as long as your DB connection and Multibyte extension are using the same character set (UTF-8), they will produce the same results by escaping the same characters as mysqli::real_escape_string.

This is based on research I did for my SQL Query Builder class:
https://github.com/twister-php/sql

<?php
/**
* Returns a string with backslashes before characters that need to be escaped.
* As required by MySQL and suitable for multi-byte character sets
* Characters encoded are NUL (ASCII 0), \n, \r, \, ', ", and ctrl-Z.
*
* @param string $string String to add slashes to
* @return $string with `\` prepended to reserved characters 
*
* @author Trevor Herselman
*/
if (function_exists('mb_ereg_replace'))
{
    function mb_escape(string $string)
    {
        return mb_ereg_replace('[\x00\x0A\x0D\x1A\x22\x27\x5C]', '\\\0', $string);
    }
} else {
    function mb_escape(string $string)
    {
        return preg_replace('~[\x00\x0A\x0D\x1A\x22\x27\x5C]~u', '\\\$0', $string);
    }
}

?>

Characters escaped are (the same as mysqli::real_escape_string):

00 = \0 (NUL)
0A = \n
0D = \r
1A = ctl-Z
22 = "
27 = '
5C = \

Note: preg_replace() is in PCRE_UTF8 (UTF-8) mode (`u`).

Enhanced version:

When escaping strings for `LIKE` syntax, remember that you also need to escape the special characters _ and %

So this is a more fail-safe version (even when compared to mysqli::real_escape_string, because % characters in user input can cause unexpected results and even security violations via SQL injection in LIKE statements):

<?php

/**
* Returns a string with backslashes before characters that need to be escaped.
* As required by MySQL and suitable for multi-byte character sets
* Characters encoded are NUL (ASCII 0), \n, \r, \, ', ", and ctrl-Z.
* In addition, the special control characters % and _ are also escaped,
* suitable for all statements, but especially suitable for `LIKE`.
*
* @param string $string String to add slashes to
* @return $string with `\` prepended to reserved characters 
*
* @author Trevor Herselman
*/
if (function_exists('mb_ereg_replace'))
{
    function mb_escape(string $string)
    {
        return mb_ereg_replace('[\x00\x0A\x0D\x1A\x22\x25\x27\x5C\x5F]', '\\\0', $string);
    }
} else {
    function mb_escape(string $string)
    {
        return preg_replace('~[\x00\x0A\x0D\x1A\x22\x25\x27\x5C\x5F]~u', '\\\$0', $string);
    }
}

?>

Additional characters escaped:

25 = %
5F = _

Bonus function:

The original MySQL `utf8` character-set (for tables and fields) only supports 3-byte sequences.
4-byte characters are not common, but I've had queries fail to execute on 4-byte UTF-8 characters, so you should be using `utf8mb4` wherever possible.

However, if you still want to use `utf8`, you can use the following function to replace all 4-byte sequences.

<?php
// Modified from: https://stackoverflow.com/a/24672780/2726557
function mysql_utf8_sanitizer(string $str)
{
    return preg_replace('/[\x{10000}-\x{10FFFF}]/u', "\xEF\xBF\xBD", $str);
}
?>

Pick your poison and use at your own risk!

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31

arnoud at procurios dot nl ¶

13 years ago

Note that this function will NOT escape _ (underscore) and % (percent) signs, which have special meanings in LIKE clauses. 

As far as I know there is no function to do this, so you have to escape them yourself by adding a backslash in front of them.

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16

zanferrari at gmail dot com ¶

4 years ago

When I submit data through Ajax I use a little function to reconvert the encoded chars to their original value. After that I do the escaping. Here the function:

   function my_htmlentities($input){
       $string = htmlentities($input,ENT_NOQUOTES,'UTF-8');
       $string = str_replace('€',chr(128),$string);
       $string = html_entity_decode($string,ENT_NOQUOTES,'ISO-8859-15');
       return $string;
   }

G.Zanferrari

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25

dave at mausner.us ¶

6 years ago

You can avoid all character escaping issues (on the PHP side) if you use prepare() and bind_param(), as an alternative to placing arbitrary string values in SQL statements.  This works because bound parameter values are NOT passed via the SQL statement syntax.

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8

James ¶

1 year ago

To escape for the purposes of having your queries made successfully, and to prevent SQLi (SQL injection)/stored and/or reflected XSS, it's a good idea to go with the basics first, then make sure nothing gets in that can be used for SQLi or stored/reflected XSS, or even worse, loading remote images and scripts.

For example:

<?php
     
     // Assume this is a simple comments form with a name and comment.

     $name = mysqli_real_escape_string($conn, $_POST['name']);
     $comments = mysqli_real_escape_string($conn, $_POST['comments']);

     // Here is where most of the action happens.  But see note below
     // on dumping back out from the database

     // We should use the ENT_QUOTES flag second parameter...
     $name = htmlspecialchars($name);
     $comments = htmlspecialchars($comments);

     $insert_sql = "INSERT INTO tbl_comments ( c_id, c_name, c_comments ) VALUES ( DEFAULT, '" . $name . "', '" . $comments . "')";

     $res = mysqli_query($conn, $insert_sql);
     if ( $res === false ) {
          // Something went wrong, handle it
     }

     // Now output page showing comments
?>

//  Assume we're in a table with each row containing a name and comment

<?php
     
     $res = mysqli_query($conn, "SELECT c_name, c_comments FROM tbl_comments ORDER BY c_name ASC");

     if ( $res === false )
          // Something went wrong

     // Or as you like...
     while ( $row = mysqli_fetch_array($res, MYSQLI_BOTH) ) {
          
          // This will output safe HTML entities if they went in
          // They will be displayed, but not interpreted
          echo "<tr><td>" . $row['c_name'] . "</td>";
          echo "<td>" . $row['c_comments'] . "</td></tr>";

          // BUT, if you make this mistake...
          echo "<tr><td>" . htmlspecialchars_decode($row['c_name']) . "</td>";
          echo "<td>" . htmlspecialchars_decode($row['c_comments']) . "</td></tr>";

          // ... then your entities will reflect back as the characters, so
          // input such as this: "><img src=x onerror=alert('xss')>
          // will display the 'xss' in an alert box in the browser.
     }

     mysqli_free_result($res);
     mysqli_close($conn);
?>

In most cases, you wouldn't want to go way overboard sanitizing untrusted user input, for instance:

<?php
     $my_input = htmlspecialchars( strip_tags($_POST['foo']) );
?>

This will junk a lot of input you might actually want, if you're rolling your own forum or comments section and it's for web developers, for example.  On the other hand, if legitimate users are never going to enter anything other than text, never HTML tags or anything else, it's not a bad idea.

The take-away is that mysqli_real_escape_string() is not good enough, and being overly-aggressive in sanitizing input may not be what you want.

Be aware that in the above example, it will protect you from sqli (run sqlmap on all your input fields and forms to check) but it won't protect your database from being filled with junk, effectively DoS'ing your Web app in the process.

So after protecting against SQLi, even if you're behind CloudFlare and take other measures to protect your databases, there's still effectively a DoS attack that could slow down your Web App for legitimate users and make it a nightmare filled with rubbish that some poor maintainer has to clean out, if you don't take other measures.

So aside from escaping your stings, and protecting against SQLi and stored/reflected XSS, and maliciously loaded images or JS, there's also checking your input to see if it makes sense, so you don't get a database full of rubbish!

It just never ends... :-)

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10

Anonymous ¶

2 years ago

If you wonder why (besides \, ' and ")  NUL (ASCII 0), \n, \r, and Control-Z are escaped: it is not to prevent sql injection, but to prevent your sql logfile to get unreadable.

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0

Lawrence DOliveiro ¶

1 month ago

Note that the “like” operator requires an *additional* level of escaping for its special characters, *on top of* that performed by mysql_escape_string. But there is no built-in function for performing this escaping. Here is a function that does it:

function escape_sql_wild($s)
  /* escapes SQL pattern wildcards in s. */
  {
    $result = array();
    foreach(str_split($s) as $ch)
      {
        if ($ch == "\\" || $ch == "%" || $ch == "_")
          {
            $result[] = "\\";
          } /*if*/
        $result[] = $ch;
      } /*foreach*/
    return
        implode("", $result);
  } /*escape_sql_wild*/

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-19

anon ¶

2 years ago

if ($_SERVER['REQUEST_METHOD'] == "GET" && isset($_GET['value'])) {
    $id = trim($link->real_escape_string($_GET['value']));
    $sql = "DELETE FROM database WHERE IDItem = $id";
    if (!$res = $link->query($sql)) {
        $_SESSION['alertify'] = 'alertify.error("' . $link->error . '")';
    } else {
        $_SESSION['alertify'] = 'alertify.success("' . $value . ' was succesfully deleted")';
    }
}

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-56

kit dot lester at mail dot com ¶

4 years ago

A PHP application I'm working on has many pages which (long story) need to share a PHP API that looks after a MySQL database. Easiest way was to have the app pages AJAX to the API .PHPs.

That means having the JavaScript of the AJAX encodeURIComponent(...) relevant bits of any data to be sent via HTTP POST and GET requests - space as %20 and so on.

But the SQL also needed real_escape_string(...) of the same data.

So I had the issue of whether to do the real_escape_string *before* or *after* encodeURIComponent? in other words in the application PHP or API PHP? Do either of the encodings mangle the other?

The real_escape_string would be "cleaner" in the API, both in principle, and because it needs an instance of mysqli class and there are are unlikely to be instances in the app.

(real_escape_string needs an instance because it's not a  *static* function - I don't know why).

But I suspect that "in the API" is the mangle-avoiding place: the JavaScript encode gets undone by the HTTP call to whichever API element, then the element can safely real_escape_string what is to be put into the database.

Comments would be appreciated.

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-89

nmmm at nmmm dot nu ¶

3 years ago

Note unlike PDO string escape, MySQLi does not include apostrophes. 

So, you probably want something like this:

    function escape($s){
        $s = $this->mysqli->real_escape_string($s);
        return "'$s'";
    }