stupid square brackets in php regex won't work!

[jonasisme]

Hi people.. i need to match aA-zZ, 0-9, _ and - and [ and ]

However everything works except [ and ]

this is what i got:

preg_match("/^[a-zA-Z0-9_-]+$/", $_POST['field']);

Please help me out as I can't find the solution!


Thanks in advance

[g1smd]

The [ and ] need to be escaped.

"/^[a-zA-Z0-9\[\]_-]+$/"

[jonasisme]

omfg.. i had that, i tried that 1000 times.. but i had put the brackets on the end.. like this "/^[a-zA-Z0-9_-\[\]]+$/" that's why it was working..

Thank you very much! Solved!

[g1smd]

It should also work with the brackets at the very end.

I moved them merely to show more clearly the required escaping. The \[\]] format makes my eyes boggle and \[\]_-] is more clear.

Also, some RegEx parsers like the hyphen to be the very last item in the list otherwise they get confused.

[lucy24]

Also, some RegEx parsers like the hyphen to be the very last item in the list otherwise they get confused.

... while others will only recognize it as a literal hyphen if it's the first item in the list ;) Literal carets, otoh, can't come first unless they are escaped. (I only know this because I've got a RegEx reference page open from another thread. Fortunately, grouping brackets tend not to get upset if you follow the "when in doubt, escape it" principle.)

[rocknbil]

Since no one's mentioned why, square brackets designate a character class. when you want to match bracket within character class, this is why it needs to be escaped.

FYI, this

preg_match("/^[a-zA-Z0-9\[\]_-]+$/", $_POST['field']);

is equivalent to this, with the i (case insensitive modifier.

preg_match("/^[a-z\d\[\]_-]+$/i", $_POST['field']);

\d being any digit.

[g1smd]

You can only use \d if your server can use PCRE.

I usually post using POSIX format, as that is more likely to work across a range of servers. If PCRE does work, it is somewhat more efficient.