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
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
$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.
Security: the default character set
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_WARNINGlevel error is generated.
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_WARNINGis generated, andFALSEis returned. Iflink_identifierisn'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.
See Also
- mysql_set_charset() - Sets the client character set
- mysql_client_encoding() - Returns the name of the character set
- addslashes() - Quote string with slashes
- stripslashes() - Un-quotes a quoted string
- The magic_quotes_gpc directive
- The magic_quotes_runtime directive
English translation
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Document created the 30/01/2003, last modified the 26/10/2018
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References
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