Need help writing a regex for usernames

user_14696108 0
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Hey so I'm looking for a regrex pattern that:

  • Allows for only two or one _ in a row but no more, can end start and have the _ in between
  • Max 20, min 3 characters
  • Allows for only one period in a row and can't start or end in a period
  • Accepts A-Z and 1-9

Some examples of passes and fails are:

.test #fail
_test #pass
_.test #pass
__test #pass
test_ #pass
te_.st #pass
te.st #pass
..test #fail

So far I have ^[\w](?!.*?\.{2})(?!.*?_{2})[\w.]{1,28}$, which works for everything but detecting the __ between and at the end of the words. Any help would be appreciated! This has been hurting my brain for hours

javascript regex
1 Answers

Allows for only one period in a row and can't start or end in a period

Negative lookahead for ^\., \.$, and \.\. from the beginning of the string

Allows for only two or one _ in a row but no more, can end start and have the _ in between

Negative lookahead for __ from the beginning of the string

Max 20, min 3 characters

After the other logic is implemented, match and consume 3-20 of the allowed characters

^(?!.*___|\.|.*\.$|.*\.\.)[a-z1-9_.]{3,20}$

https://regex101.com/r/TUjY13/2

  • ^ - From start of string:
  • (?!.*___|\.|.*\.$|.*\.\.) - Make sure match doesn't:
    • .*___ - contain triple underscores
    • \. - start with a .
    • .*\.$ - end with a .
    • .*\.\. - contain double periods
  • [a-z1-9_.]{3,20} - Match 3-20 characters in the string body using all allowed characters (case-insensitive)
user_95152070
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