Regex for string that do not start with any character of a group and do not contain any of multiple substring

Question

This might be simple, but I have lost a ridiculous amount of hours trying to get there by myself. I need to have a regex that:

1. Do not start with '_' or '-'.
2. Do not end with '_' or '-'.
3. Do not contain '__' or '--' or '_-' or '-_'.

I spent hours on a regex builder and I can't get there. I know I can find a way for each of those criteria separately but I can't have them together.

Update

I forgot to mention it must also only contain these characters [a-zA-Z0-9_-].

Answer 1

Try:

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

See: regex101

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Explanation

• ^ start of string from where...
• (?![-_]) not a - or _ is follwing
• (?: then a repetition of
  • [a-zA-Z0-9] a character that can come at any time
  • | or
  • [-_] a - or _
  • (?![-_]) as long as its not followed by another - or _
• )+
• (?<![_-])$ with the last letter also not beeing - or _