CODEWITHSUNDEEP
javascriptregex
Magro284
Magro284

Reputation: 3

Regular expression X characters long, alphanumeric but not _ and periods, but not at beginning or end

As the subject indicates, I am in need of a JavaScript Regular expression X characters long, that accepts alphanumeric characters, but not the underscore character, and also accepts periods, but not at beginning or end. Periods cannot be consecutive either.

I have been able to almost get to where I want to be searching and reading other people's questions and the answers here on Stack Overflow (such as here).

However, in my case, I need a string that has to be exactly X characters long (say 6), and can contain letters and numbers (case insensitive) and may also include periods.

Said periods cannot be consecutive and also, cannot start, or end the string.

Jd.1.4 is valid, but Jdf1.4f is not (7 characters).

/^(?:[a-z\d]+(?:\.(?!$))?)+$/i

is what I have been able to construct using examples from others, but I cannot get it to only accept strings that match the set length.

/^((?:[a-z\d]+(?:\.(?!$))?)+){6}$/i

works in that it now accepts nothing less than 6 characters, but it also happily accepts anything longer as well...

I am obviously missing something, but I do not know what it is.

Can anyone help?

Upvotes: 0

Views: 2263

Answers (2)

Casimir et Hippolyte
Casimir et Hippolyte

Reputation: 89557

Another way to do that:

/(?=.{6}$)^[a-z\d]+(?:\.[a-z\d]+)*$/i

explanation:

      (?=.{6}$)   this lookahead impose the number of characters before 
                  the end of the string
      ^[a-z\d]+   1 or more alphanumeric characters at the beginning
                  of the string
(?:\.[a-z\d]+)*   0 or more groups containing a dot followed by 1 or 
                  more alphanumerics
              $   end of the string

Upvotes: 2

Felix Kling
Felix Kling

Reputation: 816462

This should work:

/^(?!.*?\.\.)[a-z\d][a-z\d.]{4}[a-z\d]$/i

Explanation:

^             // matches the beginning of the string
(?!.*?\.\.)   // negative lookahead, only matches if there are no
              // consecutive periods (.)
[a-z\d]       // matches a-z and any digit
[a-z\d.]{4}   // matches 4 consecutive characters or digits or periods
[a-z\d]       // matches a-z and any digit
$             // matches the end of the string

Upvotes: 4

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