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PHP mysql_real_escape_string() Function


PHP MySQL Reference Complete PHP MySQL Reference

Definition and Usage

The mysql_real_escape_string() function escapes special characters in a string for use in an SQL statement

The following characters are affected:

  • \x00
  • \n
  • \r
  • \
  • '
  • "
  • \x1a

This function returns the escaped string on success, or FALSE on failure.

Syntax

mysql_real_escape_string(string,connection)

Parameter Description
string Required. Specifies the string to be escaped
connection Optional. Specifies the MySQL connection. If not specified, the last connection opened by mysql_connect() or mysql_pconnect() is used.


Tips and Notes

Note: Use this function to prevent database attack!


Example 1

<?php
$con = mysql_connect("localhost", "peter", "abc123");
if (!$con)
  {
  die('Could not connect: ' . mysql_error());
  }

// some code to get username and password

// escape username and password for use in SQL
$user = mysql_real_escape_string($user);
$pwd = mysql_real_escape_string($pwd);

$sql = "SELECT * FROM users WHERE
user='" . $user . "' AND password='" . $pwd . "'"

// more code

mysql_close($con);
?>


Example 2

Database attack. This example demonstrates what could happen if we do not use the mysql_real_escape_string() function on the username and password:

<?php
$con = mysql_connect("localhost", "peter", "abc123");
if (!$con)
  {
  die('Could not connect: ' . mysql_error());
  }

$sql = "SELECT * FROM users
WHERE user='{$_POST['user']}'
AND password='{$_POST['pwd']}'";
mysql_query($sql);

// We didn't check username and password.
// Could be anything the user wanted! Example:
$_POST['user'] = 'john';
$_POST['pwd'] = "' OR ''='";

// some code

mysql_close($con);
?>

The SQL sent would be:

SELECT * FROM users
WHERE user='john' AND password='' OR ''=''

This means that anyone could log in without a valid password!


Example 3

The correct way to do it to prevent database attack:

<?php
function check_input($value)
{
// Stripslashes
if (get_magic_quotes_gpc())
  {
  $value = stripslashes($value);
  }
// Quote if not a number
if (!is_numeric($value))
  {
  $value = "'" . mysql_real_escape_string($value) . "'";
  }
return $value;
}

$con = mysql_connect("localhost", "peter", "abc123");
if (!$con)
  {
  die('Could not connect: ' . mysql_error());
  }

// Make a safe SQL
$user = check_input($_POST['user']);
$pwd = check_input($_POST['pwd']);
$sql = "SELECT * FROM users WHERE
user=$user AND password=$pwd";

mysql_query($sql);

mysql_close($con);
?>


PHP MySQL Reference Complete PHP MySQL Reference

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