Note, that if no connection is open, mysqli_real_escape_string() will return an empty string!
(PHP 5, PHP 7, PHP 8)
mysqli::real_escape_string -- mysqli_real_escape_string — Escape caracteres especiais em uma string para uso em uma instrução SQL, levando em consideração o conjunto de caracteres atual da conexão
Estilo orientado a objetos
Estilo procedural
Esta função é usada para criar uma string SQL legal que você pode usar em uma instrução SQL. A string fornecida é codificada para produzir uma string SQL com escape, levando em consideração o conjunto de caracteres atual da conexão.
O conjunto de caracteres deve ser definido no nível do servidor ou com a função API mysqli_set_charset() para que afete mysqli_real_escape_string(). Consulte a seção de conceitos sobre conjuntos de caracteres para obter mais informações.
mysql
Somente no estilo procedural: Um objeto mysqli retornado por mysqli_connect() ou mysqli_init()
string
A string a ser escapada.
Os caracteres codificados são NUL (ASCII 0)
,
\n
, \r
, \
,
'
, "
, e
CTRL+Z.
Retorna uma string com escape.
Exemplo #1 mysqli::real_escape_string() exemplo
Estilo orientado a objetos
<?php
mysqli_report(MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT);
$mysqli = new mysqli("localhost", "my_user", "my_password", "world");
$city = "'s-Hertogenbosch";
/* esta consulta com escape $city funcionará */
$query = sprintf("SELECT CountryCode FROM City WHERE name='%s'",
$mysqli->real_escape_string($city));
$result = $mysqli->query($query);
printf("Select retornou %d linhas.\n", $result->num_rows);
/* esta consulta falhará, porque não escapamos de $city */
$query = sprintf("SELECT CountryCode FROM City WHERE name='%s'", $city);
$result = $mysqli->query($query);
Estilo procedural
<?php
mysqli_report(MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT);
$mysqli = mysqli_connect("localhost", "my_user", "my_password", "world");
$city = "'s-Hertogenbosch";
/* esta consulta com escape $city funcionará */
$query = sprintf("SELECT CountryCode FROM City WHERE name='%s'",
mysqli_real_escape_string($mysqli, $city));
$result = mysqli_query($mysqli, $query);
printf("Select retornou %d linhas.\n", mysqli_num_rows($result));
/* esta consulta falhará, porque não escapamos de $city*/
$query = sprintf("SELECT CountryCode FROM City WHERE name='%s'", $city);
$result = mysqli_query($mysqli, $query);
Os exemplos acima produzirão algo semelhante a:
Select retornou 1 linhas. Fatal error: Uncaught mysqli_sql_exception: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 's-Hertogenbosch'' at line 1 in...
Note, that if no connection is open, mysqli_real_escape_string() will return an empty string!
For percent sign and underscore I use this:
<?php
$more_escaped = addcslashes($escaped, '%_');
?>
You can avoid all character escaping issues (on the PHP side) if you use prepare() and bind_param(), as an alternative to placing arbitrary string values in SQL statements. This works because bound parameter values are NOT passed via the SQL statement syntax.
Note that this function will NOT escape _ (underscore) and % (percent) signs, which have special meanings in LIKE clauses.
As far as I know there is no function to do this, so you have to escape them yourself by adding a backslash in front of them.
Presenting several UTF-8 / Multibyte-aware escape functions.
These functions represent alternatives to mysqli::real_escape_string, as long as your DB connection and Multibyte extension are using the same character set (UTF-8), they will produce the same results by escaping the same characters as mysqli::real_escape_string.
This is based on research I did for my SQL Query Builder class:
https://github.com/twister-php/sql
<?php
/**
* Returns a string with backslashes before characters that need to be escaped.
* As required by MySQL and suitable for multi-byte character sets
* Characters encoded are NUL (ASCII 0), \n, \r, \, ', ", and ctrl-Z.
*
* @param string $string String to add slashes to
* @return $string with `\` prepended to reserved characters
*
* @author Trevor Herselman
*/
if (function_exists('mb_ereg_replace'))
{
function mb_escape(string $string)
{
return mb_ereg_replace('[\x00\x0A\x0D\x1A\x22\x27\x5C]', '\\\0', $string);
}
} else {
function mb_escape(string $string)
{
return preg_replace('~[\x00\x0A\x0D\x1A\x22\x27\x5C]~u', '\\\$0', $string);
}
}
?>
Characters escaped are (the same as mysqli::real_escape_string):
00 = \0 (NUL)
0A = \n
0D = \r
1A = ctl-Z
22 = "
27 = '
5C = \
Note: preg_replace() is in PCRE_UTF8 (UTF-8) mode (`u`).
Enhanced version:
When escaping strings for `LIKE` syntax, remember that you also need to escape the special characters _ and %
So this is a more fail-safe version (even when compared to mysqli::real_escape_string, because % characters in user input can cause unexpected results and even security violations via SQL injection in LIKE statements):
<?php
/**
* Returns a string with backslashes before characters that need to be escaped.
* As required by MySQL and suitable for multi-byte character sets
* Characters encoded are NUL (ASCII 0), \n, \r, \, ', ", and ctrl-Z.
* In addition, the special control characters % and _ are also escaped,
* suitable for all statements, but especially suitable for `LIKE`.
*
* @param string $string String to add slashes to
* @return $string with `\` prepended to reserved characters
*
* @author Trevor Herselman
*/
if (function_exists('mb_ereg_replace'))
{
function mb_escape(string $string)
{
return mb_ereg_replace('[\x00\x0A\x0D\x1A\x22\x25\x27\x5C\x5F]', '\\\0', $string);
}
} else {
function mb_escape(string $string)
{
return preg_replace('~[\x00\x0A\x0D\x1A\x22\x25\x27\x5C\x5F]~u', '\\\$0', $string);
}
}
?>
Additional characters escaped:
25 = %
5F = _
Bonus function:
The original MySQL `utf8` character-set (for tables and fields) only supports 3-byte sequences.
4-byte characters are not common, but I've had queries fail to execute on 4-byte UTF-8 characters, so you should be using `utf8mb4` wherever possible.
However, if you still want to use `utf8`, you can use the following function to replace all 4-byte sequences.
<?php
// Modified from: https://stackoverflow.com/a/24672780/2726557
function mysql_utf8_sanitizer(string $str)
{
return preg_replace('/[\x{10000}-\x{10FFFF}]/u', "\xEF\xBF\xBD", $str);
}
?>
Pick your poison and use at your own risk!
If you wonder why (besides \, ' and ") NUL (ASCII 0), \n, \r, and Control-Z are escaped: it is not to prevent sql injection, but to prevent your sql logfile to get unreadable.
Caution when escaping the % and _ wildcard characters. According to an often overlooked note at the bottom of:
https://dev.mysql.com/doc/refman/5.7/en/string-literals.html#character-escape-sequences
the escape sequences \% and \_ will ONLY be interpreted as % and _, *if* they occur in a LIKE! (Same for MySQL 8.0)
In regular string literals, the escape sequences \% and \_ are treated as those two character pairs. So if those escape sequences appear in a WHERE "=" instead of a WHERE LIKE, they would NOT match a single % or _ character!
Consequently, one MUST use two "escape" functions: The real-escape-string (or equivalent) for regular string literals, and an amended escape function JUST for string literals that are intended to be used in LIKE.
Note that the “like” operator requires an *additional* level of escaping for its special characters, *on top of* that performed by mysql_escape_string. But there is no built-in function for performing this escaping. Here is a function that does it:
function escape_sql_wild($s)
/* escapes SQL pattern wildcards in s. */
{
$result = array();
foreach(str_split($s) as $ch)
{
if ($ch == "\\" || $ch == "%" || $ch == "_")
{
$result[] = "\\";
} /*if*/
$result[] = $ch;
} /*foreach*/
return
implode("", $result);
} /*escape_sql_wild*/
I think two additional characters need to be removed or escaped to protect from injection: ` (accent grave) and ; (semicolon). Accent grave could be used to inject into table and key names, terminating them too early (if user input is allowed as table or key names), and semicolon could be used to insert additional statements into an SQL statement. Always use ` (accent grave) to surround table, key, and column names, and always use ' (apostrophe) to surround column values in SQL statements, especially if the names or values can ever contain spaces.