^(([^<>()[\]\\.,;:\s@\"]+(\.[^<>()[\]\\.,;:\s@\"]+)*)|(\".+\"))
    @((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\])|(([a-zA-Z\-0-9]+\.)
  +[a-zA-Z]{2,}))$

I could only understand parts of the regex but not the entire expression , like

([^<>()[\]\\.,;:\s@\"]+(\.[^<>()[\]\\.,;:\s@\"]+)*)

match one or more characters that's are not the characters

<>()[\]\\.,;:\s@\"  \\  Not sure what this [\]\\  and \s@\ means

I could understand some of the other parts as well but not as a single entity.

^(([^<>()[\]\\.,;:\s@\"]+(\.[^<>()[\]\\.,;:\s@\"]+)*)|(\".+\"))
    @((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\])|(([a-zA-Z\-0-9]+\.)
  +[a-zA-Z]{2,}))$

I could only understand parts of the regex but not the entire expression , like

([^<>()[\]\\.,;:\s@\"]+(\.[^<>()[\]\\.,;:\s@\"]+)*)

match one or more characters that's are not the characters

<>()[\]\\.,;:\s@\"  \\  Not sure what this [\]\\  and \s@\ means

I could understand some of the other parts as well but not as a single entity.

• javascript
• regex
• validation

• Where did you got that from? Is it a string passed to new RegExp, or did you omit literal delimiters? – Bergi Commented May 2, 2013 at 18:14
• I was working with javascript validations , and came across it where it it was being used to test email Address I tried to understand it but in vain – Sushanth -- Commented May 2, 2013 at 18:16
• myezapp./apps/dev/regexp/show.ws Plug it in here for a visual explination of the capture groups ect. Here is yours: tinyurl./ccuqrwk – asawyer Commented May 2, 2013 at 18:16
• The entries with a backslash in front of them are escaped characters that would have other meanings. \] is just the ] character, as that would normally end the class, and \\ is an escaped backslash, so just means the backslash itself. \s is a special character class of whitespace. – Orbling Commented May 2, 2013 at 18:17
• 3 If you use a regex like this in your code, and I have to e along after you and figure it out, I WILL figure out where you live! “Always code as if the guy who ends up maintaining your code is a violent psychopath who knows where you live.” – DOK Commented May 2, 2013 at 18:21

3 Answers 3

Here you go:

^(
    (
        [^<>()[\]\\.,;:\s@\"]+ // Disallow these characters any amount of times
        (
            \. // Allow dots
            [^<>()[\]\\.,;:\s@\"]+ // Disallow these characters any amount of times
        )* // This group must occur once or more
    )
    | // or
    (\".+\") // Anything surrounded by quotes (Is this even legal?)
)
@ // At symbol is litterally that
(
    // IP address
    (
        \[ // Allows square bracket
        [0-9]{1,3} // 1 to three digits (for an IP address
        \. // Allows dot
        [0-9]{1,3} // 1 to three digits (for an IP address
        \. // Allows dot
        [0-9]{1,3} // 1 to three digits (for an IP address
        \. // Allows dot
        [0-9]{1,3} // 1 to three digits (for an IP address
        \] // Square bracket
    ) 
    | // OR a domain name
    (
        ([a-zA-Z\-0-9]+\.) // Valid domain characters are a-zA-Z0-9 plus dashes
        +
        [a-zA-Z]{2,} // The top level (anything after the dot) must be at least 2 chars long and only a-zA-Z
    )
)$

Here is an easy to see illustration from debuggex.

"Not sure what this [\]\\ and \s@\" means"

\] is an escaped ]
\\ is an escaped \
\s is any white space
@ is @
\" is an escaped "

"what does the + mean"

+ means "one or more" of what precedes the +