Trouble with simple PHP profanity filter

Question

I am writing a simple profanity filter in PHP. Can anyone tell my why, in the following code, the filter works (it will print [explicit]) for the $vowels array and not the $lines array which I constructing from a text file?

 function clean($str){

$handle = fopen("badwords.txt", "r");
if ($handle) {
   while (!feof($handle)) {
       $array[] = fgets($handle, 4096);
   }
   fclose($handle);
}

$vowels = array("a", "e", "i", "o", "u", "A", "E", "I", "O", "U");

$filter = "[explicit]";
$clean = str_replace($array, $filter, $str);
return $clean;
 }

When using $vowels in replace of $array, it works except for lowercase vowels which return:

 [[expl[explicit]c[explicit]t]xpl[explicit]c[explicit]t]

 instead of 

 [explicit]

Not sure why that is going on, either.

Any ideas?

Thanks!

score 1 · Answer 1 · answered Aug 01 '09 at 06:05

1

Because the output of the filter contains lower case vowels, which are also the characters you're filtering. Namely you're creating a feedback loop.

answered Aug 01 '09 at 06:05

Don Neufeld

22,720
11
51
50

davethegr8 · Answer 2 · 2009-08-01T15:44:33.060

1

First off, file_get_contents is a much simpler function to read a file into a variable.

$badwords = explode("\n", file_get_contents('badwords.txt');

Second, preg_replace offers much more flexible string replacement options. - http://us3.php.net/preg_replace

foreach($badwords as $word) {
    $patterns[] = '/'.$word.'/';
}

$replacement = '[explicit]';

$output = preg_replace($patterns, $replacement, $input);

edited Aug 01 '09 at 15:44

answered Aug 01 '09 at 06:09

davethegr8

11,323
5
36
61

1

That's a pretty poor code example You've provided as only the last word in the badwords.txt will be replaced with the text '[explicit]'. If anything you should simply remove the foreach and do the following: $output = preg_replace($badwords, $replacement, $input); – Andy Aug 01 '09 at 06:47
1

@andy - haha, oops. It was late last night and I forgot a []. :) – davethegr8 Aug 01 '09 at 15:45

score 1 · Accepted Answer · answered Aug 01 '09 at 07:08

I modified Davethegr8's solution to get the following working example:

 function clean($str){

global $clean_words; 

$replacement = '[explicit]';

if(empty($clean_words)){
    $badwords = explode("\n", file_get_contents('badwords.txt'));

    $clean_words = array();

    foreach($badwords as $word) {
        $clean_words[]= '/(\b' . trim($word) . '\b)/si';
    }
}

$out = preg_replace($clean_words, $replacement, $str);
return $out;
 }

Trouble with simple PHP profanity filter

3 Answers3

Linked