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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 Descriptionstring 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_escape_string, which prepends backslashes to the following characters:
NULL, \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));
?>
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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 $query;
?>
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The query sent to MySQL:
SELECT * FROM users WHERE name='aidan' AND password='' OR ''='' |
This would allow anyone to log in without a valid password.
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Example 3. A "Best Practice" query
Using mysql_real_escape_string() around each variable
prevents SQL Injection. This example demonstrates the "best practice"
method for querying a database, independent of the
Magic Quotes setting.
<?php
// Quote variable to make safe
function quote_smart($value)
{
// Stripslashes
if (get_magic_quotes_gpc()) {
$value = stripslashes($value);
}
// Quote if not integer
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);
?>
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The query will now execute correctly, and SQL Injection attacks will not work.
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NotesNote:
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:
mysql_real_escape_string() does not escape
% and _. These are wildcards in
MySQL if combined with LIKE, GRANT,
or REVOKE.
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