preg_match include forward slash

Question

This is the function I have that checks if the entered security question and/or answer contain malicious characters: ``` function validate_input($field) { $ErrorMessage = ""; $field = preg_replace("/[\s]+is/", '', $field); if(preg_match("/^[A-Za-z0-9'?!-\s]+$/", $field ) ===0) { $ErrorMessage .= "

Potentially malicious characters found in: " . $field . ", please enter only alphanumeric characters

"; } return $ErrorMessage; } ``` When I enter something like "What's up?" for the question, it comes back with an error. When I do a var_dump on ($field) it comes back as "What\'s up?". So how can I include the forward slash as an acceptable character?

Accepted Answer

It would seem that you have the "magic quote" feature of PHP active, which shouldn't be for security reasons: all the escaping of user inserted data should be done by your own code.

Anyway, if you want to keep things as they are now, replace your

```
preg_match("/^[A-Za-z0-9'?!-\s]+$/", $field)
```

with

```
preg_match("/^[A-Za-z0-9'?!-\s\\]+$/", $field )
```

the quadruple \ is there because you need to escape it both, for being in a string delimited with double quotes and for being in a regex.

preg_match include forward slash

Solution

Problem