Question

I have a pattern with a small list of words that are illegal to use as nicknames set in a pattern variable like this:

$pattern = webmaster|admin|webadmin|sysadmin

Using preg_match, how can I achieve so that nicknames with these words are forbidden, but registering something like “admin2” or “thesysadmin” is allowed?

This is the expression I have so far:

preg_match('/^['.$pattern.']/i','admin');

// Should not be allowed

Note: Using a \b didn’t help much.

Answer 1

What about not using regex at all ?

And working with explode and in_array ?

For instance, this would do :

$pattern = 'webmaster|admin|webadmin|sysadmin';
$forbidden_words = explode('|', $pattern);

It explodes your pattern into an array, using | as separator.

And this :

$word = 'admin';
if (in_array($word, $forbidden_words)) {
    echo "<p>$word is not OK</p>";
} else {
    echo "<p>$word is OK</p>";
}

will get you

admin is not OK

Whereas this (same code ; only the word changes) :

$word = 'admin2';
if (in_array($word, $forbidden_words)) {
    echo "<p>$word is not OK</p>";
} else {
    echo "<p>$word is OK</p>";
}

will get you

admin2 is OK

This way, no need to worry about finding the right regex, to match full-words : it’ll just match exact words 😉

---

Edit : one problem might be that the comparison will be case-sensitive 🙁

Working with everything in lowercase will help with that :

$pattern = strtolower('webmaster|admin|webadmin|sysadmin');  // just to be sure ;-)
$forbidden_words = explode('|', $pattern);

$word = 'aDMin';
if (in_array(strtolower($word), $forbidden_words)) {
    echo "<p>$word is not OK</p>";
} else {
    echo "<p>$word is OK</p>";
}

Will get you :

aDMin is not OK

(I saw the ‘i‘ flag in the regex only after posting my answer ; so, had to edit it)

---

Edit 2 : and, if you really want to do it with a regex, you need to know that :

• ^ marks the beginning of the string
• and $ marks the end of the string

So, something like this should do :

$pattern = 'webmaster|admin|webadmin|sysadmin';

$word = 'admin';
if (preg_match('#^(' . $pattern . ')$#i', $word)) {
    echo "<p>$word is not OK</p>";
} else {
    echo "<p>$word is OK</p>";
}

$word = 'admin2';
if (preg_match('#^(' . $pattern . ')$#i', $word)) {
    echo "<p>$word is not OK</p>";
} else {
    echo "<p>$word is OK</p>";
}

Parentheses are probably not necessary, but I like using them, to isolate what I wanted.

And, you’ll get the same kind of output :

admin is not OK

admin2 is OK

You probably don’t want to use [ and ] : they mean “any character that is between us”, and not “the whole string that is between us”.

And, as the reference : manual of the preg syntax 😉