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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

## 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 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.

## See Also

mysql_client_encoding()
addslashes()
stripslashes()
The magic_quotes_gpc directive
The magic_quotes_runtime directive

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