Regular expression for Password match in PHP and Javascript

Question

I have built a regular expression for password policy match, but it is not working as expected

/((?=. \\d)(?=. [az])(?=. [AZ])(?=. [@#\\$%!])(?!(.)*\\1{2,}).{6,20})/

Password must satisfy below rules -> must have 1 digit -> must have 1 upper case letter -> must have 1 lower case letter -> must have 1 special character from given list -> minimum 6 character long -> maximum 20 character long -> Not more than 2 identical characters`

So it matches

aDm!n1, Adw1n@

but it must not match below aaaD!n1, teSt@111

I have searched for this regular expression and found "(?!(.)*\\1{2,})" is not working properly

I am not getting why it is not working even though it has lookahead negative assertion.

Thanks in advance

Answer 1

You must need to provide start and end anchors.

^(?=.*\d)(?=.*[a-z])(?=.*[A-Z])(?=.*[@#\$%\!])(?!.*(.).*\1.*\1).{6,20}$

DEMO

To match the strings which isn't contain more than two duplicate characters, you need to use a negative lookahead like (?!.*(.).*\\1.*\\1) which asserts that the string we are going to match wouldn't contain not more than two duplicate characters.

• (?!) Negative lookahead which checks if there isn't
• .* Any character zero or more times.
• (.) A single character was captured.
• .* Any character zero or more times.
• \\1 Reference to the group index 1. That is, it refers to the character which are already captured by group 1.
• .* Any character zero or more times.
• \\1 Back-referencing to the character which was present inside the group index 1.

Code:

> var re = /^(?=.*\d)(?=.*[a-z])(?=.*[A-Z])(?=.*[@#\$%\!])(?!.*(.).*\1.*\1).{6,20}$/;
undefined
> re.test('aDm!n1')
true
> re.test('Adw1n@')
true
> re.test('tetSt@11')
false

Answer 2

(?:(?=.*\d)(?=.*[a-z])(?=.*[A-Z])(?=.*[@#\$%!])(?!.*(.).*\1.*\1).{6,20})

You need this.See demo.

http://regex101.com/r/hQ9xT1/22

Your regex was failing cos

(?!(.)*\\1{2,}) will not work as it find consecutive repeated characters and not any character which is three times or more.So use (?!.*(.).*\\1.*\\1) .

var re = /^(?:(?=.*\d)(?=.*[a-z])(?=.*[A-Z])(?=.*[@#\$%!])(?!.*(.).*\1.*\1).{6,20})$/gm;
var str = 'aaaD!n1\nteSt@111\naDm!n1\nAdw1n@';
var m;

while ((m = re.exec(str)) != null) {
if (m.index === re.lastIndex) {
re.lastIndex++;
}
// View your result using the m-variable.
// eg m[0] etc.
}