[ACCEPTED]-RegEx for allowing alphanumeric at the starting and hyphen thereafter-regex

Accepted answer

Score: 17

If you do not want to match mutiple dashes 2 after eachother:

^[a-zA-Z0-9]+(-[a-zA-Z0-9]+)*$

This will match: a, a-a, aaa-a, aaa-a-aaa-a-aaa-a, etc
But 1 not: -, -a, a-, a--a, a-a-a-, a-a--a, etc.

Score: 8

^[a-zA-Z0-9][a-zA-Z0-9-]*[a-zA-Z0-9]$

Score: 6

I would propose:

^[a-zA-Z0-9]([a-zA-Z0-9-]*[a-zA-Z0-9])?$

This also matches strings 1 of the length 1.

Score: 5

Here is the POSIX + look-akead variant of 10 doing it:

^[[:alnum:]](?:[[:alnum:]-](?!-$))*$

This also allows just one character 9 as a match. It is not so readable, though. ;-)

Note 8 that [[:alnum:]] is a shorthand predefined character 7 class equivalent to [a-zA-Z0-9], being more efficient, but 6 otherwise interchangeable. Not every regex 5 flavor knows these POSIX classes, use the 4 traditional form if you like.

Here is one 3 that does not allow multiple consecutive 2 hyphens, and it is shorter:

^(?:[[:alnum:]]+(?:-(?!$))?)+$

and it's non-POSIX 1 form:

^(?:[a-zA-Z0-9]+(?:-(?!$))?)+$

Source: stackoverflow.com

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