<?php

$string = 'foo';

if (preg_match('/[\'^£$%&*()}{@#~?><>,|=_+¬-]/', $string))
{
    // one or more of the 'special characters' found in $string
}

How about using a regex:

if (preg_match('/[^a-zA-Z]+/', $your_string, $matches))
{
  echo 'Oops some number or symbol encountered !!';
}
else
{
  // Everything fine... carry on
}

this is how i do it :

if (preg_match('/[^a-zA-Z\d]/', $string)) {
//$string contains special characters, do something.
}

Assuming that you mean html entities when you say "special chars", you can use this:

<?php
$table = get_html_translation_table(HTML_ENTITIES, ENT_COMPAT, 'UTF-8');
$chars = implode('', array_keys($table));

if (preg_match("/[{$chars}]+/", $string) === 1) {
    // special chars in string
}

get_html_translation_table gets all the possible html entities. If you only want the entities that the function htmlspecialchars converts, then you can pass HTML_SPECIALCHARS instead of HTML_ENTITIES. The return value of get_html_translation_table is an array of (html entity, escaped entity) pairs.

Next, we want to put all the html entities in a regular expression like [&"']+, which will match any substring containing one of the characters inside square brackets of length 1 or more. So we use array_keys to get the keys of the translation table (the unencoded html entities), and implode them together into a single string.

Then we put them into the regular expression and use preg_match to see if the string contains any of those characters. You can read more about regular expression syntax at the PHP docs.

You can do that with a regex :

<?php

$string = 'classone insertclass_182 classtwo';    
$regex = '/insertclass_([0-9]*)/';    
$result = preg_match($regex, $string, $matches);    
var_dump($matches);

It will return :

array(2) {
  [0] =>
  string(15) "insertclass_182"
  [1] =>
  string(3) "182"
}

you can do like this

<?php
$illegal = "#$%^&*()+=-[]';,./{}|:<>?~";
echo (false === strpbrk($YourCsvVarible, $illegal)) ? 'Allowed' : "Disallowed";
?>

Note : strpbrk(string,charlist) it will return false when string not contain character which you passed in 2ed argument and see i have passed all character in $illegal = "#$%^&*()+=-[]';,./{}|:<>?~"; if you need more http://php.net/manual/en/function.strpbrk.php

A concise way to do it with your two data structures would be:

count( array_intersect( str_split($my_string), $special_chars ) )

That would also tell you how many of the special characters are in the string.

You could otherwise write a loop for your character list and manually probe with strpos.

The least effort would be converting your special character list into a regex charclass and testing against the string.

No need for all that. Just use one bracket group, negate it (be prepending a ^), and use the return value directly:

function is_clean ($string) {
    return ! preg_match("/[^a-z\d_-]/i", $string);
}

Here's a quote from the PHP docs:

Return Values
preg_match() returns 1 if the pattern matches given subject, 0 if it does not, or FALSE if an error occurred.

In the regex above, we're looking for any characters in the string that are not in the bracket group. If none are found, preg_match will return 0 (which when negated will result in true). If any of those characters are found, 1 will be returned and negated to false.