function mysql-real-escape-string - Escapes special characters in a string for use in an 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 no connection is found or established, an E_WARNING level error 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
// We didn't check $_POST['password'], it could be anything the user wanted! For example:
$_POST['username'] = 'aidan';
$_POST['password'] = "' OR ''='";

// 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);

// 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.

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.

mysql_real_escape_string

Description

Parameters

Return Values

Examples

Notes

See Also