preg_match() is evaluating my regex incorrently - php

Question

My regex validation is producing true when it should be false. I've tried this exact example using online regex validators, and it is always rejected except in my code. Am I doing something wrong?
$name = "1NTH";
preg_match("/[A-Z][A-Z][A-Z][A-Z]?/",$name);
This exact example is evaluating to true.

Answer 1

You're getting the correct behaviour, as you're asking for three capital letters eventually followed by a fourth one.
You probably want to use this regex:
/^[A-Z][A-Z][A-Z][A-Z]?$/
(note the ^, start of line, and $ end of line) as it explicitly requires that the capital letters must be all the content of the text line.

Answer 2

This is because it is true. It contains [A-Z] characters.
You're missing the anchors to start your regex from the start of the string to finish of the string.
^[A-Z][A-Z][A-Z][A-Z]?$

Answer 3

There's nothing wrong with your regex. It is valid based on the rule you specified.
Let's do it one step at a time:
[A-Z] means match exactly 1 upper case alphabet.
[A-Z]? means, match either 0 or 1 upper case alphabet.
See what's going on? If not, move on.
[A-Z][A-Z][A-Z] means match exactly 3 upper case alphabets. (1 for each [A-Z] rule)
[A-Z][A-Z][A-Z][A-Z]? means the first three characters must be an upper case alphabet. The last one can either be 0 or 1 upper case alphabet.
In your example, 1NTH contains exactly 3 upper case alphabets, which is correct. You didn't put any restrictions on whether it should contain number or not, whether before or after the 3 alphabets. And the last [A-Z]?? Well, that's optional, right? (see rule #2)

Answer 4

The standard PHP regular expression engine checks if the the string contains the pattern, and is not an exact match. That differs to, for example, the standard Java regular expression engine.
You should use ^ and $, which match respectively the beginning and the end of a string. Both are zero-length assertions.
$name = "1NTH";
preg_match("/^[A-Z]{3}[A-Z]?$/", $name);
PS: I have optimized your regular expression by using the quantifier {3}, which matches three subsequent occurrences of the preceding character or group.

Answer 5

Accoring to PHP Manual:
preg_match() returns 1 if the pattern matches given subject, 0 if it does not, or FALSE if an error occurred.
In your example, there must be 3 obligatory and 1 optional capital letter. So, the match is due.

Answer 6

As stribizhev said, your regex matches since you're asking for more than 3 letters which are found in $name. I assume you want to reject "1NTH" because it starts with a digit. That means you have to add an anchor saying "from the start" (\A).
Also, the 3 repeated [A-Z] can be summarized by adding a repeat-counter. So the whole statement should be: \A[A-Z]{3,}

Answer 7

You have given like this,
$name = "1NTH";
preg_match("/[A-Z][A-Z][A-Z][A-Z]?/",$name);
In your code some please change this below code
$name = "1NTH";
preg_match("/[A-Z][A-Z][A-Z][A-Z]?$/",$name);
you have missed '$' in end of preg string.
i have checked and it's working perfectly to your requirement.
See this link,and you also test once in this link. Click Here