Need Regex Help - regex

Question

Can anybody help me with a regex? I have a string with digits like:
X024123099XYAAXX99RR
I need a regex to check if a user has inserted the correct information. The rule should have also a fallback that the input is checked from left to right.
For example, when tested these inputs should return TRUE:
X024
X024123099X
X024123099XYA
X024123099XYAAXX99R
And these ones should return FALSE:
XX024
X02412AA99X
X024123099XYAAXX9911
And so on. The regex must check for the correct syntax, beginning from the left.
I have something like that, but this seems not to be correct:
\w\d{0,12}\w{0,6}\d{0,2}\w{0,2}
Big thanks for any help (I'm new to regex)

Answer 1

You could take OpenSauce's regex and then hack it to pieces to allow partial matches:
^[A-Z](\d{0,9}$|\d{9}([A-Z]{0,6}$|[A-Z]{6}(\d{0,2}$|\d{2}([A-Z]{0,2}$))))
It's not pretty but as far as I can tell it encodes your requirements.
Essentially I took each case of something like \d{9} and replaced it with something like (\d{0,9}$|\d{9}<rest of regex>).
I added ^ and $ because otherwise it will match substrings in an otherwise invalid string. For example, it will see an invalid string like XX024 and think it is okay because it contains X024.

Answer 2

If I understand you correctly, your strings should match the regex
[A-Z]\d{9}[A-Z]{6}\d{2}[A-Z]{2}
but you also want to check if a string could be a prefix of a matching string, is that correct? You might be able to express this in a single regex, but I can't think of a way to do so that's easy to read.
You haven't said which language you're using, but if your language gives you a way to tell if the end of the input string was reached while checking the regex, that would give you an easy way to get what you want. E.g. in java, the method Matcher.hitEnd tells you whether the end was reached, so the below code:
static Pattern pattern = Pattern.compile( "[A-Z]\\d{9}[A-Z]{6}\\d{2}[A-Z]{2}" );
static Matcher matcher = pattern.matcher( "" );
public static void main(String[] args) {
String[] strings = {
"X024",
"X024123099X",
"X024123099XYA",
"X024123099XYAAXX99R",
"XX024",
"X02412AA99X",
"X024123099XYAAXX9911"
};
for ( String string : strings ) {
out.format( "%s %s\n", string, inputOK(string) ? "OK" : "not OK" );
}
}
static boolean inputOK(String input) {
return matcher.reset(input).matches() || matcher.hitEnd();
}
gives output:
X024 OK
X024123099X OK
X024123099XYA OK
X024123099XYAAXX99R OK
XX024 not OK
X02412AA99X not OK
X024123099XYAAXX9911 not OK