How to avoid a hyphen from splitting a regex?

RazzFazz :

I'm writing a simple android app for saving your favorite games in a list.

In the first screen a user has to enter his gamertag (as a String). The gamertag should only contain letters from a-z (uppercase and lowercase), numbers (0-9) and underscores/hpyhens (_ and -).

I can get it to work with an underscore in every position or a hyphen at the beginning. But if the String contains a hyphen in the middle it gets "split" into two pieces and if the hyphen is at the end, it stands alone.

I came up with this regex:

[a-zA-Z0-9_\-]\w+

in java it looks a little different because the \ needs to be escaped:

[a-zA-Z0-9_\\-]\\w+

Gamertags that should validate:

- GamerTag
- Gamer_Tag
- _GamerTag
- GamerTag_
- -GamerTag
- Gamer-Tag
- GamerTag-

Gamertags that shouldn't validate:

- !GamerTag
- Gamer%Tag
- Gamer Tag

Gamertags that should validate, but my regex fails:

- Gamer-Tag
- GamerTag-

The fourth bird :

Your pattern [a-zA-Z0-9_\-]\w+ matches 1 character out of the character class followed by 1+ times a word character \w which does not match a -.

You could repeat the character class 1+ times where the hyphen is present and if the hyphen is at the end of the character class you don't have to eacape it.

[a-zA-Z0-9_-]+

The Gamer-Tag does not get split but has 2 matches. The character class matches G and the \w+ matches amer. Then in the next match the character class matches - and \w+ matches Tag.

If those are the only values allowed, you could use anchors ^ to assert the start and $ to assert the end of the string.

^[a-zA-Z0-9_-]+$

Regex demo