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
<?php // 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
<?php // 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 $query; ?>
The query sent to MySQL:
SELECT * FROM users WHERE user='aidan' AND password='' OR ''=''
This would allow anyone to log in without a valid password.
Example 3. A "Best Practice" query
Using mysql_real_escape_string() around each variable
prevents SQL Injection. This example demonstrates the "best practice"
method for querying a database, independent of the
Magic Quotes setting.
<?php // Quote variable to make safe function quote_smart($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.
