正则表达式，以字母数字和连字符开头，在字符串中下划线

Question

I'm trying to write a regexp in golang that matches strings that start as alphanumeric and can have an underscore or hyphen after, but not starting with a hyphen or underscore.

Here is what I could come up with, but this matches alphanumeric and hyphen underscore anywhere

[A-Za-z0-9_-]

So something like sea-food would match or seafood or sea_food, but not -seafood nor _seafood.

Answer 1

You need to use a ^ to indicate the start of the string and $ for the end, and then use two character classes:

^[A-Za-z0-9][A-Za-z0-9_-]*$

To disallow hyphens and underscores at the end of the string as well try:

^[A-Za-z0-9]([A-Za-z0-9_-]*[A-Za-z0-9])?$