Question

I’ve tried several regex combinations to figure out this, but some or the condition fails,

I have an input string, that could only contain a given set of defined characters

lets say A , B or C in it.

how do I match for something like this?

ABBBCCC — isMatch True

AAASDFDCCC — isMatch false

ps. I’m using C#

Answer 1

 ^[ABC]+$

Should be enough: that is using a Character class or Character Set.

The Anchors ‘^’ and ‘$’ would be there only to ensure the all String contains only those characters from start to end.

Regex.Match("ABACBA", "^[ABC]+$"); // => matches

Meaning: a Character Set will not guarantee the order of he characters matched.

Regex.Match("ABACBA", "^A+B+C+$"); // => false

Would guarantee the order