Regex - Match ( only ) words with mixed chars

Question

i'm writing my anti spam/badwors filter and i need if is possible,

to match (detect) only words formed by mixed characters like: fr1&nd$ and not friends

is this possible with regex!?

best regards!

Answer 1

Of course it's possible with regex! You're not asking to match nested parentheses! :P

But yes, this is the kind of thing regular expressions were built for. An example:

/\S*[^\w\s]+\S*/

This will match all of the following:

@ss
as$
a$s
@$s
a$$
@s$
@$$

It will not match this:

ass

Which I believe is what you want. How it works:

\S* matches 0 or more non-space characters. [^\w\s]+ matches only the symbols (it will match anything that isn't a word or a space), and matches 1 or more of them (so a symbol character is required.) Then the \S* again matches 0 or more non-space characters (symbols and letters).

If I may be allowed to suggest a better strategy, in Perl you can store a regex in a variable. I don't know if you can do this in PHP, but if you can, you can construct a list of variables like such:

$a = /[aA@]/ # regex that matches all a-like symbols
$b = /[bB]/
$c = /[cC(]/
# etc...

Or:

$regex = array( 'a' => /[aA@]/, 'b' => /[bB]/, 'c' => /[cC(]/, ... );

So that way, you can match "friend" in all its permutations with:

/$f$r$i$e$n$d/

Or:

/$regex['f']$regex['r']$regex['i']$regex['e']$regex['n']$regex['d']/

Granted, the second one looks unnecessarily verbose, but that's PHP for you. I think the second one is probably the best solution, since it stores them all in a hash, rather than all as separate variables, but I admit that the regex it produces is a bit ugly.

Answer 2

It is possible, you will not have very pretty regex rules, but you can match basically any pattern that you can describe using regex. The tricky part is describing it.

I would guess that you would have a bunch of regex rules to detect bad words like so:

To detect fr1&nd$, friends, fr**nd* you can use a regex like:

/fr[1iI*][&eE]nd[s$Sz]/

Doing something like this for each rule will find all the variations of possible characters in the brackets. Pick up a regex guide for more info.

(I'm assuming for a badwords filter you would want friend as well as frie**, you may want to mask the bad word as well as all possible permutations)

Answer 3

Didn't test this thoroughly, but this should do it:

(\w+)*(?<=[^A-Za-z ])

Answer 4

You could build some regular expressions like the following:

\p{L}+[\d\p{S}]+\S*

This will match any sequence of one or more letters (\p{L}+, see Unicode character preferences), one or more digits or symbols ([\d\p{S}]+) and any following non-whitespace characters \S*.

$str = 'fr1&nd$ and not friends';
preg_match('/\p{L}+[\d\p{S}]+\S*/', $str, $match);
var_dump($match);