Regex pattern for username validation

Question

I am trying to put together a regex pattern to validate usernames in our account creation PS script. The format of our usernames are FirstName.LastName. We do accept hyphens,apostrophes and numbers also but only as follows:

Firstname - letters only, hyphens, apostrophes also accepted.

LastName - alphanumeric accepted, hyphens and apostrophes also accepted.

The below regex seems to work but it doesn't work for if the username begins or ends with an apostrophe/hyphen as they are valid characters.

"^[a-zA-Z]+-*'*[a-zA-Z]+\.[a-zA-Z]+-*'*[0-9a-zA-Z]+$"

How would i amend the above to also ensure the string doesn't match if it begins or ends with an apostrophe or hyphen? i'd also like to limit hyphens and apostrophes to only 1 consecutive (E.g. "sh-aun" and not "sha--un, "sh'aun" and not "sh''aun") in both the firstname part and lastname part.

Any help would be much appreciated. Thanks in advance.

Answer 1

• PowerShell's regex-matching is case-insensitive by default, so [a-z] is sufficient to match both lowercase and uppercase letters.

• [a-z] only matches ASCII (non-accented) letters; to also allow accented letters, use \p{L} instead.

To allow multiple - and ' per first and last name (but neither at the start nor at the end, and not consecutively):

"^[a-z]+(?:[-'][a-z]+)*\.[a-z]+(?:[-'][a-z0-9]+)*$"

• For an explanation of this regex and interactive experimentation with it, see this regex101.com page.

• Example:

  # -> $true
  "shaun.o'brien-Thompson" -match "^[a-z]+(?:[-'][a-z]+)*\.[a-z]+(?:[-'][a-z0-9]+)*$"
  

---

To allow just one (internal) - or ', replace the * with ?:

"^[a-z]+(?:[-'][a-z]+)?\.[a-z]+(?:[-'][a-z0-9]+)?$"

Answer 2

You are using both hyphen and apostrophe in the first character set, and it is allowing it to match the words starting with these characters. The following one should work

^[a-zA-Z]+-?'?[a-zA-Z]+\.[0-9a-zA-Z]+-?'?[a-zA-Z]+$

? allows the engine to match zero or one occurence of the preceding token