Regex to match a-z spaces, character limit, only first letter capitalized - php

Question

I need some help with a regex. I'm terrible at this.
Rules:
Only letters a through z and spaces
Minimum 2 letters
Maximum 30 letters
Each word must be at least 2 letters
Only the first letter of each word may be capital but the first letter must always be capital
My attempt:
^[A-Z][a-z]{2,30}$
I'm using this in PHP.

Answer 1

Okay, so let's try solving requirements 1 to 3 first. If you mean 2 to 30 characters it's as simple as this:
^[a-zA-Z ]{2,30}$
Now for the other requirements. Let's handle those alone. Point 4 requires each word to be of the form [a-zA-Z][a-z]*. To make sure that each word has at least two letters, we can simply turn the * into a + (which means 1 or more repetitions). If we insert explicit spaces around these, that makes sure that the [a-z]+ cannot be followed directly by a capital letter:
^[A-Z][a-z]+(?:[ ]+[a-zA-Z][a-z]+)*$
Note that I treated the first word separately.
Finally, how do we combine the two? By putting one into a lookahead. I'm going for the counting here:
^(?=[a-zA-Z ]{2,30}$)[A-Z][a-z]+(?:[ ]+[a-zA-Z][a-z]+)*$
This works because, after the input is checked against the lookahead the engine resets it "cursor" to where it started (the beginning of the string) and continues matching as usual. This way we can run two passes over the input, checking for independent conditions.
Finally, note that the lookahead requirement simply translates to the string's length. In such a case it would be easier (and most often better) to check this separately:
$len = strlen($input)
if ($len < 2 || $len > 30)
// report error about string length
else if (!preg_match('/^[A-Z][a-z]+(?:[ ]+[a-zA-Z][a-z]+)*$/', $input))
// report error about pattern
else
// process input
This makes it much easier to give sensible error messages depending on which condition was violated.

Answer 2

Let's try this:
^[A-Z]((?<= )[A-Z]|[a-z ]){2,29}$
[A-Z] -- a capital letter
(
(?<= )[A-Z] -- either a capital letter preceded by a space
| -- or
[a-z ] -- a lowercase letter or a space
){2,29} -- 2 to 29 times (plus the initial capital)
You will need to use the PCRE (not ereg_*) for the lookbehind to work.
"My name Is bob"
↑ ↑ ↑
| | \-- this is a "(?<= )[A-Z]"
| \--- this is a "[a-z]"
\---- this is a "[ ]"
"naMe"
↑
\-- this is NOT a "(?<= )[A-Z]" (a character before the [A-Z] is not a space)
EDIT: damn, you added the "Each word must be at least 2 letters". Use m.buettner's.