Check if a string contain multiple specific words

You can't do something like this:

if (strpos($data, 'bad || naughty') !== false) {

instead, you can use regex:

if(preg_match("/(bad|naughty|other)/i", $data)){
 //one of these string found
}

strpos does search the exact string you pass as second parameter. If you want to check for multiple words you have to resort to different tools

regular expressions

if(preg_match("/\b(bad|naughty)\b/", $data)){
    echo "Found";
}

(preg_match return 1 if there is a match in the string, 0 otherwise).

multiple str_pos calls

if (strpos($data, 'bad')!==false or strpos($data, 'naughty')!== false) {
    echo "Found";
}

explode

if (count(array_intersect(explode(' ', $data),array('bad','naugthy')))) {
    echo "Found";
}

The preferred solution, to me, should be the first. It is clear, maybe not so efficient due to the regex use but it does not report false positives and, for example, it will not trigger the echo if the string contains the word badmington

The regular expression can become a burden to create if it a lot of words (nothing you cannot solve with a line of php though $regex = '/\b('.join('|', $badWords).')\b/';

The second one is straight forward but can't differentiate bad from badmington.

The third split the string in words if they are separated by a space, a tab char will ruins your results.

For this, you will need Regular Expressions and the preg_match function.

Something like:

if(preg_match('(bad|naughty)', $data) === 1) { } 

The reason your attempt didn't work

Regular Expressions are parsed by the PHP regex engine. The problem with your syntax is that you used the || operator. This is not a regex operator, so it is counted as part of the string.

As correctly stated above, if it's counted as part of the string you're looking to match: 'bad || naughty' as a string, rather than an expression!