Question

I have never really studied regex so do not really ungerstand it

I have the following regex expression that tests email addresses

^([\\w]+)(\\.[\\w]+)*@([\\w\\-]+\\.){1,5}([A-Za-z]){2,4}$

when i enter [e-mail] it fails but when i enter [e-mail] it works… can anyone explain why this is?

EDIT

Have been looking into the code and would this regex fail for the above email addresses?

^\\w[-._\\w]*\\w@\\w[-._\\w]*\\w\\.\\w{2,6}$

Answer 1

That regexp will not fail for .cat but match .com you must have something other issues causing the behavior you are seeing, here is an explanation of the regex:

^([\w]+)(\.[\w]+)*@([\w-]+\.){1,5}([A-Za-z]){2,4}$/

^ Start of string

1st Capturing group ([\w]+) 
Char class [\w] infinite to 1 times matches one of the following chars: \w
\w Word character [a-zA-Z_\d] 

2nd Capturing group (\.[\w]+) infinite to 0 times 
\. Literal .
Char class [\w] infinite to 1 times matches one of the following chars: \w
\w Word character [a-zA-Z_\d] 
@ Literal @

3rd Capturing group ([\w-]+\.) 5 to 1 times 
Char class [\w-] infinite to 1 times matches one of the following chars: \w-
\w Word character [a-zA-Z_\d] 
\. Literal .

4th Capturing group ([A-Za-z]) 4 to 2 times 
Char class [A-Za-z] matches one of the following chars: A-Za-z

$ End of string

And the second will also accept both given the right escaping (in most languages the double backslashes would cause both not to match):

/^\w[-._\w]*\w@\w[-._\w]*\w\.\w{2,6}$/

^ Start of string

\w Word character [a-zA-Z_\d] 
Char class [-._\w] infinite to 0 times matches one of the following chars: -._\w
\w Word character [a-zA-Z_\d] 
\w Word character [a-zA-Z_\d] 

@ Literal @

\w Word character [a-zA-Z_\d] 
Char class [-._\w] infinite to 0 times matches one of the following chars: -._\w

\w Word character [a-zA-Z_\d] 
\w Word character [a-zA-Z_\d] 

\. Literal .

\w 6 to 2 times Word character [a-zA-Z_\d] 

$ End of string