Replace Characters Not Listed In A Whitelist Array

[matthewtbaker]

Hi,

 

I have created an array with symbols that I'd like to allow in a string of text.

 

$symbols[] = '>'; // Greater Than or Open Angle Bracket
$symbols[] = '<'; // Less Than or Close Angle Bracket
$symbols[] = '/'; // Forward Slash
$symbols[] = '\\'; // Back Slash
$symbols[] = '&'; // Ampersand
$symbols[] = '£'; // Pound Sterling
$symbols[] = '$'; // Dollar
$symbols[] = '\"'; // Quotation Marks
$symbols[] = '\''; // Apostrophe
$symbols[] = '#'; // Hash
$symbols[] = ' '; // Space
$symbols[] = '.'; // Period

 

I would now like to use something like str_replace or preg_replace (whichever is best) to replace any character that is not included within the array $symbols with "".

 

I know there are other ways to filter characters but it isn't a suitable solution considering who will be maintaining it... :-\

 

I'm hoping for something like; but obviously a working way.

$myText = str_replace(!$symbols, "", $myText;
$myText = preg_replace(!$symbols, "", $myText;

 

 

Thank you for your help.

[matthewtbaker]

Further to my original question I have found a similar solution but it does not work properly.

 

$symbols = array(); //WHITELIST OF SYMBOLS

 $symbols[] = 'a-z'; // Lowercase A to Z
 $symbols[] = 'A-Z'; // Uppercase A to Z
 $symbols[] = '0-9'; // Numbers 0 to 9

 $symbols[] = '>'; // Greater Than or Open Angle Bracket
 $symbols[] = '<'; // Less Than or Close Angle Bracket
 $symbols[] = '/'; // Forward Slash
 $symbols[] = '\\'; // Back Slash
 $symbols[] = '&'; // Ampersand
 $symbols[] = '£'; // Pound Sterling
 $symbols[] = '$'; // Dollar
 $symbols[] = '\"'; // Quotation Marks
 $symbols[] = '\''; // Apostrophe
 $symbols[] = '#'; // Hash
 $symbols[] = ' '; // Space
 $symbols[] = '\.'; // Period
 $symbols[] = '\,'; // Comma
 $symbols[] = '_'; // Underscore
 $symbols[] = '-'; // Hyphen or Dash
 $symbols[] = '@'; // At
 $symbols[] = '%'; // Percentage
 $symbols[] = '?'; // Question Mark
 $symbols[] = '*'; // Asterisk
 $symbols[] = '('; // Open Bracket
 $symbols[] = ')'; // Close Bracket
 $symbols[] = '+'; // Plus
 $symbols[] = '='; // Equals
 $symbols[] = '{'; // Open Brace
 $symbols[] = '}'; // Close Brace
 $symbols[] = '['; // Open Bracket
 $symbols[] = ']'; // Close Bracket
 $symbols[] = '~'; // Tilde

 $myText = preg_replace("/[^" . $symbols . "]^" . $symbols . "]?/iu", "", $myText);

 

It does not keep all of my white list symbols.

Edited October 8, 2012 by matthewtbaker

[ManiacDan]

Use the second example and do:

 

         $myText = preg_replace("/[^" . preg_quote(implode('',$symbols), '/') . "]/i", "", $myText);

 

[matthewtbaker]

Thanks Maniac!

 

I have had some problems with my:

 

$symbols[] = 'a-z'; // Lowercase A to Z
$symbols[] = 'A-Z'; // Uppercase A to Z
$symbols[] = '0-9'; // Numbers 0 to 9

 

So have had to list each letter individually. Do you know how I can just have a simple a-z, 0-9 in my array?

 

Much appreciated.

 

 

Also if you could be explain why the implode is needed for the line to work I'd be most grateful.

 

Matt

[ManiacDan]

listing them individually is the easiest way, but at this point you're allowing most of the ascii range. Might as well make a blacklist, or specify your ranged by hand using an ascii chart.

 

If you use an array as a string, it becomes the word "Array." Implode turns an array into a string so you can actually see the values.

[xyph]

listing them individually is the easiest way, but at this point you're allowing most of the ascii range. Might as well make a blacklist, or specify your ranged by hand using an ascii chart.

 

If you use an array as a string, it becomes the word "Array." Implode turns an array into a string so you can actually see the values.

 

I think it's preg_quote that's messing up the ranges (\-).

 

IMO, using a blacklist is a bad idea unless you're limiting all input to the ASCII range, and even then it would be pretty big.

 

A solution could be to keep ranges in a separate array, and not preg_quote those.

[matthewtbaker]

Thanks for the information chaps. I'm going to stick with the White-List approach as I don't want to the risk missing a character.

[kicken]

You could avoid listing them out by-hand by using the range function:

$symbols = array(); //WHITELIST OF SYMBOLS

$symbols += range('a', 'z'); // Lowercase A to Z
$symbols += range('A', 'Z'); // Uppercase A to Z
$symbols += range('0', '9'); // Numbers 0 to 9

$symbols[] = '>'; // Greater Than or Open Angle Bracket
$symbols[] = '<'; // Less Than or Close Angle Bracket
...

 

[ManiacDan]

I think it's preg_quote that's messing up the ranges (\-).

It definitely is. Kicken's solution is the most correct, if OP is really just trying to whitelist 75% of the ascii chart and disallow diacritical marks and utf-8 characters.

 

[xyph]

Well, there's 256 valid ASCII characters, so he's nowhere near half-way.

[matthewtbaker]

You could avoid listing them out by-hand by using the range function:

$symbols = array(); //WHITELIST OF SYMBOLS

$symbols += range('a', 'z'); // Lowercase A to Z
$symbols += range('A', 'Z'); // Uppercase A to Z
$symbols += range('0', '9'); // Numbers 0 to 9

$symbols[] = '>'; // Greater Than or Open Angle Bracket
$symbols[] = '<'; // Less Than or Close Angle Bracket
...

 

 

$symbols += range('a', 'z');

 

This is spot on, many many thanks! Finally 3 days of constant code hacking has ended with clean fresh code. Amen.

[Jessica]

I wasn't aware you could add to an array like that. (+=) That actually works? I've always used array_merge. Or is that new?

 

$symbols = array(); //WHITELIST OF SYMBOLS

$symbols += range('a', 'z'); // Lowercase A to Z
$symbols += range('A', 'Z'); // Uppercase A to Z
$symbols += range('0', '9'); // Numbers 0 to 9

$symbols[] = '>'; // Greater Than or Open Angle Bracket
$symbols[] = '<'; // Less Than or Close Angle Bracket
print_r($symbols);

When I run that code, I get:

Array ( [0] => a [1] => b [2] => c [3] => d [4] => e [5] => f [6] => g [7] => h [8] => i [9] => j [10] => k [11] => l [12] => m [13] => n [14] => o [15] => p [16] => q [17] => r [18] => s [19] => t [20] => u [21] => v [22] => w [23] => x [24] => y [25] => z [26] => > [27] => < )

Edited October 8, 2012 by Jessica

[kicken]

You can use + with array's. I always forget it's not the same as array_merge though, it's a union. array_merge is what you'd need here.

$symbols = array(); //WHITELIST OF SYMBOLS

$symbols = array_merge($symbols, range('a', 'z')); // Lowercase A to Z
$symbols = array_merge($symbols, range('A', 'Z')); // Uppercase A to Z
$symbols = array_merge($symbols, range('0', '9')); // Numbers 0 to 9

$symbols[] = '>'; // Greater Than or Open Angle Bracket
$symbols[] = '<'; // Less Than or Close Angle Bracket
print_r($symbols);

Edited October 8, 2012 by kicken