How to write a RegEx to check for a certain, specific number of characters?

Question

I am trying to test a string for a state code, the regex I have is

^A[LKSZRAEP]|C[AOT]|D[EC]|F[LM]|G[AU]|HI|I[ADLN]|K[SY]|LA|M[ADEHINOPST]|N[CDEHJMVY]|O[HKR]|P[ARW]|RI|S[CD]|T[NX]|UT|V[AIT]|W[AIVY]$

The issue is, if I have something like "CTA12" as a test string, it will get a match of CT. How can I modify my regex to make it only match state codes that are not part of a larger string?

Answer 1

Your use of anchors with alternation is incorrect, ^AB|DC$ means "strings that start with AB or end with DC ". To get the ^ and $ to both apply to each element of the alternation, you need to put the alternation in a group, for example ^(AB|DC)$ .

Try changing your regex to the following:

^(A[LKSZRAEP]|C[AOT]|D[EC]|F[LM]|G[AU]|HI|I[ADLN]|K[SY]|LA|M[ADEHINOPST]|N[CDEHJMVY]|O[HKR]|P[ARW]|RI|S[CD]|T[NX]|UT|V[AIT]|W[AIVY])$

The alternative to using a group is to put the ^ and $ as a part of each element in the alternation, for example ^AB$|^DC$ , but that would make your regex significantly longer so a group is the way to go.