Need help with Regular Expression to Match Blood Group

Question

I'm trying to come up with a regex that helps me validate a Blood Group field - which should accept only A[+-], B[+-], AB[+-] and O[+-]. Here's the regex I came up with (and tested using Regex Tester): ``` [A|B|AB|O][\+|\-] ``` Now this pattern successfully matches A,B,O[+-] but fails against AB[+-]. Can anyone please suggest a regex that'll serve my purpose? Thanks, m^e

Accepted Answer

Try:

```
(A|B|AB|O)[+-]
```

Using square brackets defines a character class, which can only be a single character. The parentheses create a grouping which allows it to do what you want. You also don't need to escape the `+-` in the character class, as they don't have their regexy meaning inside of it.

As you mentioned in the comments, if it is a string you want to match against that has the exact values you are looking for, you might want to do this:

```
^(A|B|AB|O)[+-]$
```

Without the start of string and end of string anchors, things like "helloAB+asdads" would match.

Need help with Regular Expression to Match Blood Group

Solution

Problem