Using RegEx to Count the Length of the String in a Matched Pattern

Question

I've been trying to resolve this all day.

Here are the requirements:
- I want to match strings that optionally starts with " _ "
- Should then continue with one or more case-insensitive alphabet
- Should then contain an optional " _ " or " - " followed by case-insensitive alphanumeric characters (This step should match at lease once).
- Then it may optionally end with " _ "

The above requirements are not a problem 'cos I achieved that with:

/_?[A-Za-z]([-_]?[A-Za-z0-9])+_?/

The above RegEx matches:

user_
usEr-nAme
uSer_naMe-Two_
_Userna-Me_tHree-and-four

THE PROBLEM
How do I make it match only 6 to 25 characters?

I Tried

/(_?[A-Za-z]([-_]?[A-Za-z0-9])+_?){6,25}/

but it still matches string less than 6 like Use-r

James Buck · Accepted Answer · 2016-01-30 01:45:11Z

4

Put a lookahead assertion at the start:

(?=^.{6,25}$)_?[A-Za-z]([-_]?[A-Za-z0-9])+_?

Demo here.

edited Jan 30, 2016 at 1:45

answered Jan 30, 2016 at 1:42

James Buck

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3 Comments

Andreas Louv Over a year ago

I guess you want: (?=.{6,25}$)?

Andreas Louv Over a year ago

and optional also ^ at the start or \b, not exactly sure what OP wants.

DLastCodeBender Over a year ago

Thank you! Just what I needed!

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