Regular Expression for delimited email address

Question

i am looking for a regular express to validate a list of email addresses like the following

test1@abd.com;test.test@abc.com;test3@test.com

and

test1@abd.com;test.test@abc.com;test3@test.com;

optional ";" at the end of the list.

thanks,

Answer 1

Update

Don't. Split on the delimiter and validate each one separately. I would also recommend setting a match timeout and/or non-backtracking flag to prevent excessive CPU usage when matching.

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Original Answer

From: http://regexlib.com/RETester.aspx?regexp_id=1007

^(([a-zA-Z0-9_\-\.]+)@([a-zA-Z0-9_\-\.]+)\.([a-zA-Z]{2,5}){1,25})+([;.](([a-zA-Z0-9_\-\.]+)@([a-zA-Z0-9_\-\.]+)\.([a-zA-Z]{2,5}){1,25})+)*$

Answer 2

“You call that a knife???” —Crocodile Dundee

Actually, all those are very poor patterns for matching a mail address. To strictly validate an RFC 5322 mail address with zero false negatives and zero false positives, you need this precise pattern:

  (?x)

  (?(DEFINE)

     (?<address>         (?&mailbox) | (?&group))
     (?<mailbox>         (?&name_addr) | (?&addr_spec))
     (?<name_addr>       (?&display_name)? (?&angle_addr))
     (?<angle_addr>      (?&CFWS)? < (?&addr_spec) > (?&CFWS)?)
     (?<group>           (?&display_name) : (?:(?&mailbox_list) | (?&CFWS))? ; (?&CFWS)?)
     (?<display_name>    (?&phrase))
     (?<mailbox_list>    (?&mailbox) (?: , (?&mailbox))*)

     (?<addr_spec>       (?&local_part) \@ (?&domain))
     (?<local_part>      (?&dot_atom) | (?&quoted_string))
     (?<domain>          (?&dot_atom) | (?&domain_literal))
     (?<domain_literal>  (?&CFWS)? \[ (?: (?&FWS)? (?&dcontent))* (?&FWS)?
                                   \] (?&CFWS)?)
     (?<dcontent>        (?&dtext) | (?&quoted_pair))
     (?<dtext>           (?&NO_WS_CTL) | [\x21-\x5a\x5e-\x7e])

     (?<atext>           (?&ALPHA) | (?&DIGIT) | [!#\$%&'*+-/=?^_`{|}~])
     (?<atom>            (?&CFWS)? (?&atext)+ (?&CFWS)?)
     (?<dot_atom>        (?&CFWS)? (?&dot_atom_text) (?&CFWS)?)
     (?<dot_atom_text>   (?&atext)+ (?: \. (?&atext)+)*)

     (?<text>            [\x01-\x09\x0b\x0c\x0e-\x7f])
     (?<quoted_pair>     \\ (?&text))

     (?<qtext>           (?&NO_WS_CTL) | [\x21\x23-\x5b\x5d-\x7e])
     (?<qcontent>        (?&qtext) | (?&quoted_pair))
     (?<quoted_string>   (?&CFWS)? (?&DQUOTE) (?:(?&FWS)? (?&qcontent))*
                          (?&FWS)? (?&DQUOTE) (?&CFWS)?)

     (?<word>            (?&atom) | (?&quoted_string))
     (?<phrase>          (?&word)+)

     # Folding white space
     (?<FWS>             (?: (?&WSP)* (?&CRLF))? (?&WSP)+)
     (?<ctext>           (?&NO_WS_CTL) | [\x21-\x27\x2a-\x5b\x5d-\x7e])
     (?<ccontent>        (?&ctext) | (?&quoted_pair) | (?&comment))
     (?<comment>         \( (?: (?&FWS)? (?&ccontent))* (?&FWS)? \) )
     (?<CFWS>            (?: (?&FWS)? (?&comment))*
                         (?: (?:(?&FWS)? (?&comment)) | (?&FWS)))

     # No whitespace control
     (?<NO_WS_CTL>       [\x01-\x08\x0b\x0c\x0e-\x1f\x7f])

     (?<ALPHA>           [A-Za-z])
     (?<DIGIT>           [0-9])
     (?<CRLF>            \x0d \x0a)
     (?<DQUOTE>          ")
     (?<WSP>             [\x20\x09])
   )

   (?&address)  # finally, match a mail address

I discuss this in more detail in this answer.

That needs a Perl Compatible Regular Expression (PCRE) library, or Perl itself, to work properly. I cannot guarantee that perl incompatible pattern engines will correctly handle the recursion.

Answer 3

@Evan's answer is close, but the expression matches these scenarios which are invalid:

1. a@test.comb@test.comc@test.com (no delimiters)
2. a@test.com;b@test.com.c@test.com (period . accepted as delimiter)
3. a@test.com;b@test.comc@test.com (only 1st delimiter matched - extension of problem #1)

To fix these (and simplify a little bit), I made these changes:

1. Removed the 3rd + sign, and the outer parens () surrounding the first email address.
2. Change [;.] to a plain ; delimiter - I actually changed that part to ;[ ]{0,1} because I wanted the expression to match spaces after the semi-colon delimiter.
3. Similar to #1, remove the final + sign in the expression, and the outer parens () between the delimiter (step #2) and the final closing paren with the star after it - )*

Here is the final expression (allowing an optional space after the ; delimiter:

/^([a-zA-Z0-9_\-\.]+)@([a-zA-Z0-9_\-\.]+)\.([a-zA-Z]{2,5}){1,25}(;[ ]{0,1}([a-zA-Z0-9_\-\.]+)@([a-zA-Z0-9_\-\.]+)\.([a-zA-Z]{2,5}){1,25})*$/

Answer 4

I use this:

^(([a-zA-Z0-9_\-\.]+)@([a-zA-Z0-9_\-\.]+)\.([a-zA-Z]{2,5}){1,25}(($)|( *;+ *$)|( *;+ *(?=[a-zA-Z0-9_\-\.]))))*$

https://regexr.com/3gth7

Answer 5

I needed to allow for the presence of white space around the delimiter, so I used this modification of Evan Mulawski's answer:

^(([a-zA-Z0-9_\-\.]+)@([a-zA-Z0-9_\-\.]+)\.([a-zA-Z]{2,5}){1,25})+(\s*[;.]\s*(([a-zA-Z0-9_\-\.]+)@([a-zA-Z0-9_\-\.]+)\.([a-zA-Z]{2,5}){1,25})+)*$

Test it at: http://regexlib.com/RETester.aspx?regexp_id=13126

Answer 6

(?:[a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:\.[a-z0-9!#$%&'*+/=?^_`{|}~-]+)*|"(?:[\x01-\x08\x0b\x0c\x0e-\x1f\x21\x23-\x5b\x5d-\x7f]|\\[\x01-\x09\x0b\x0c\x0e-\x7f])*")@(?:(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?|\[(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?|[a-z0-9-]*[a-z0-9]:(?:[\x01-\x08\x0b\x0c\x0e-\x1f\x21-\x5a\x53-\x7f]|\\[\x01-\x09\x0b\x0c\x0e-\x7f])+)\])