mysql_real_escape_string

(PHP 4 >= 4.3.0, PHP 5)
mysql_real_escape_string -- Escapes special characters in a string for use in a SQL statement

Description

string mysql_real_escape_string ( string unescaped_string [, resource link_identifier] )

Escapes special characters in the unescaped_string, taking into account the current character set of the connection so that it is safe to place it in a mysql_query(). If binary data is to be inserted, this function must be used.
mysql_real_escape_string() calls MySQL's library function mysql_real_escape_string, which prepends backslashes to the following characters: \x00, \n, \r, \, ', " and \x1a.
This function must always (with few exceptions) be used to make data safe before sending a query to MySQL.

Parameters

unescaped_string: The string that is to be escaped.
link_identifier: The MySQL connection. If the link identifier is not specified, the last link opened by mysql_connect() is assumed. If no such link is found, it will try to create one as if mysql_connect() was called with no arguments. If by chance no connection is found or established, an E_WARNING level warning is generated.

Return Values

Returns the escaped string, or FALSE on error.

Examples

Example 1. Simple mysql_real_escape_string() example

 // Connect

$link = mysql_connect('mysql_host', 'mysql_user', 'mysql_password')

    OR die(mysql_error());



// Query

$query = sprintf("SELECT * FROM users WHERE user='%s' AND password='%s'",

            mysql_real_escape_string($user),

            mysql_real_escape_string($password));

?>

Example 2. An example SQL Injection Attack

 // Query database to check if there are any matching users

$query = "SELECT * FROM users WHERE user='{$_POST['username']}' AND password='{$_POST['password']}'";

mysql_query($query);



// We didn't check $_POST['password'], it could be anything the user wanted! For example:

$_POST['username'] = 'aidan';

$_POST['password'] = "' OR ''='";



// This means the query sent to MySQL would be:

echo $query;

?>

The query sent to MySQL:

SELECT * FROM users WHERE user='aidan' AND password='' OR ''=''

This would allow anyone to log in without a valid password.

Example 3. A "Best Practice" query
Using mysql_real_escape_string() around each variable prevents SQL Injection. This example demonstrates the "best practice" method for querying a database, independent of the Magic Quotes setting.

 // Quote variable to make safe

function quote_smart($value)

{

    // Stripslashes

    if (get_magic_quotes_gpc()) {

        $value = stripslashes($value);

    }

    // Quote if not a number or a numeric string

    if (!is_numeric($value)) {

        $value = "'" . mysql_real_escape_string($value) . "'";

    }

    return $value;

}



// Connect

$link = mysql_connect('mysql_host', 'mysql_user', 'mysql_password')

    OR die(mysql_error());



// Make a safe query

$query = sprintf("SELECT * FROM users WHERE user=%s AND password=%s",

            quote_smart($_POST['username']),

            quote_smart($_POST['password']));



mysql_query($query);

?>

The query will now execute correctly, and SQL Injection attacks will not work.

Notes

Note: A MySQL connection is required before using mysql_real_escape_string() otherwise an error of level E_WARNING is generated, and FALSE is returned. If link_identifier isn't defined, the last MySQL connection is used.

Note: If magic_quotes_gpc is enabled, first apply stripslashes() to the data. Using this function on data which has already been escaped will escape the data twice.

Note: If this function is not used to escape data, the query is vulnerable to SQL Injection Attacks.

Note: mysql_real_escape_string() does not escape % and _. These are wildcards in MySQL if combined with LIKE, GRANT, or REVOKE.

Think different