PHP Manual
MySQL Functions
Escapes special characters in a string for use in an SQL statement

mysql_real_escape_string

(PHP 4 >= 4.3.0, PHP 5)

mysql_real_escape_string — Escapes special characters in a string for use in an SQL statement

Warning This extension was deprecated in PHP 5.5.0, and it was removed in PHP 7.0.0. Instead, the MySQLi or PDO_MySQL extension should be used. See also MySQL: choosing an API guide and related FAQ for more information. Alternatives to this function include:

Description

mysql_real_escape_string ( string $unescaped_string [, resource $link_identifier = NULL ] ) : string

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.

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

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() had been 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.

Errors/Exceptions

Executing this function without a MySQL connection present will also emit E_WARNING level PHP errors. Only execute this function with a valid MySQL connection present.

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 mysql_real_escape_string() requires a connection example

This example demonstrates what happens if a MySQL connection is not present when calling this function.

<?php// We have not connected to MySQL$lastname = "O'Reilly";$_lastname = mysql_real_escape_string($lastname);$query = "SELECT * FROM actors WHERE last_name = '$_lastname'";var_dump($_lastname);var_dump($query);?>

The above example will output something similar to:

Warning: mysql_real_escape_string(): No such file or directory in /this/test/script.php on line 5
Warning: mysql_real_escape_string(): A link to the server could not be established in /this/test/script.php on line 5

bool(false)
string(41) "SELECT * FROM actors WHERE last_name = ''"

Example #3 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.

Php/docs/function.mysql-real-escape-string

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