Regex help please..

[Ian Branch 127]

Hi Team,

Regex is one of those mysteries I have never fathomed. :-(

I have the following code..

function ValidEmail(const EmailAddress: string): Boolean;
const
  EMAIL_REGEX = '^((?>[a-zA-Z\d!#$%&''*+\-/=?^_`{|}~]+\x20*|"((?=[\x01-\x7f])' + '[^"\\]|\\[\x01-\x7f])*"\x20*)*(?<angle><))?((?!\.)' +
    '(?>\.?[a-zA-Z\d!#$%&''*+\-/=?^_`{|}~]+)+|"((?=[\x01-\x7f])' + '[^"\\]|\\[\x01-\x7f])*")@(((?!-)[a-zA-Z\d\-]+(?<!-)\.)+[a-zA-Z]' +
    '{2,}|\[(((?(?<!\[)\.)(25[0-5]|2[0-4]\d|[01]?\d?\d))' + '{4}|[a-zA-Z\d\-]*[a-zA-Z\d]:((?=[\x01-\x7f])[^\\\[\]]|\\' +
    '[\x01-\x7f])+)\])(?(angle)>)$';
begin
  Result := IsMatch(EmailAddress, EMAIL_REGEX);
end;

I don't recall exactly where I found it, apologies to the author, and it has served me well.

It works well for single email address entries.

How can it be modified so that it will parse multiple email addresses separated by a ';'?

e.g. myemail@here.com;youremail@there.com.au

With possible expansion to three or more email addresses in the future.

I will be most grateful for any solution.

 

Regards & TIA,

Ian

[corneliusdavid 214]

I think I would split the string on semicolons and run the regex on each individual address.

function ValidEmail(const EmailAddress: string): Boolean;
const
  EMAIL_REGEX = '^((?>[a-zA-Z\d!#$%&''*+\-/=?^_`{|}~]+\x20*|"((?=[\x01-\x7f])' + '[^"\\]|\\[\x01-\x7f])*"\x20*)*(?<angle><))?((?!\.)' +
    '(?>\.?[a-zA-Z\d!#$%&''*+\-/=?^_`{|}~]+)+|"((?=[\x01-\x7f])' + '[^"\\]|\\[\x01-\x7f])*")@(((?!-)[a-zA-Z\d\-]+(?<!-)\.)+[a-zA-Z]' +
    '{2,}|\[(((?(?<!\[)\.)(25[0-5]|2[0-4]\d|[01]?\d?\d))' + '{4}|[a-zA-Z\d\-]*[a-zA-Z\d]:((?=[\x01-\x7f])[^\\\[\]]|\\' +
    '[\x01-\x7f])+)\])(?(angle)>)$';
var
  Emails: TStringList;
begin
  Result := True;

  Emails := TStringList.Create;
  try
    Emails.Delimiter := ';';
    Emails.StrictDelimiter := True;
    Emails.DelimitedText := EmailAddress;
    for var i := 0 to Emails.Count - 1 do
      if not IsMatch(Emails[i], EMAIL_REGEX) then
      begin
        Result := False;
        Break;
      end;
  finally
    Emails.Free;
  end;
end;

 

[Ian Branch 127]

Hi David,

Doh!!  This is where I face palm myself and berate myself for not thinking of that. 😞

Thank you for pointing out my inadequacy. 🙂

 

Regards & Tks again,

Ian

 

[corneliusdavid 214]

LOL! We all get stuck in a train of thought once in a while! I've definitely been there. 😎

[Darian Miller 361]

Why don't you extract the email addresses and process them individually?

 

Also look at:  https://github.com/Xor-el/EmailValidationPascal

 

 

[Attila Kovacs 629]

  EMAIL_REGEX = '^((((?>[a-zA-Z\d!#$%&''*+\-/=?^_`{|}~]+\x20*|"((?=[\x01-\x7f])' + //
    '[^"\\]|\\[\x01-\x7f])*"\x20*)*(?<angle><))?((?!\.)' + //
    '(?>\.?[a-zA-Z\d!#$%&''*+\-/=?^_`{|}~]+)+|"((?=[\x01-\x7f])' + //
    '[^"\\]|\\[\x01-\x7f])*")@(((?!-)[a-zA-Z\d\-]+(?<!-)\.)+[a-zA-Z]' + //
    '{2,}|\[(((?(?<!\[)\.)(25[0-5]|2[0-4]\d|[01]?\d?\d))' + //
    '{4}|[a-zA-Z\d\-]*[a-zA-Z\d]:((?=[\x01-\x7f])[^\\\[\]]|\\' + //
    '[\x01-\x7f])+)\])(?(angle)>))(;\S)*)+$';

eventually

 

 

[Ian Branch 127]

Hi Attila,

Thank you for your contribution.

Given that I have no idea about regex I can only wonder at what you have done.

 

Regards,

Ian

[Fr0sT.Brutal 900]

...and then International Domain Names come into chat

[Timothy.Prinsloo 0]

@Fr0sT.Brutal speaking of International Domain Names any ideas
 

I still have to validate the

1. Latin alphabet with diacritics       Pelé@example.com
2. Greek alphabet                           δοκιμή@παράδειγμα.δοκιμή
3. Traditional Chinese characters     我買@屋企.香港
4. Japanese characters                    二ノ宮@黒川.日本 
5. Cyrillic characters                        медведь@с-балалайкой.рф 
6. Devanagari characters                संपर्क@डाटामेल.भारत   

using the same RegEx as OP

[Lars Fosdal 1791]

On 9/19/2021 at 11:53 PM, Attila Kovacs said:

  EMAIL_REGEX = '^((((?>[a-zA-Z\d!#$%&''*+\-/=?^_`{|}~]+\x20*|"((?=[\x01-\x7f])' + //
    '[^"\\]|\\[\x01-\x7f])*"\x20*)*(?<angle><))?((?!\.)' + //
    '(?>\.?[a-zA-Z\d!#$%&''*+\-/=?^_`{|}~]+)+|"((?=[\x01-\x7f])' + //
    '[^"\\]|\\[\x01-\x7f])*")@(((?!-)[a-zA-Z\d\-]+(?<!-)\.)+[a-zA-Z]' + //
    '{2,}|\[(((?(?<!\[)\.)(25[0-5]|2[0-4]\d|[01]?\d?\d))' + //
    '{4}|[a-zA-Z\d\-]*[a-zA-Z\d]:((?=[\x01-\x7f])[^\\\[\]]|\\' + //
    '[\x01-\x7f])+)\])(?(angle)>))(;\S)*)+$';

eventually

 

 

You have a problem.
You apply RegEx to solve the problem.
You now have two problems.

[Attila Kovacs 629]

17 minutes ago, Lars Fosdal said:

You now have two problems.

\p{L}+([-+.']\p{L}+)*@\p{L}+([-.]\p{L}+)*\.\p{L}+([-.]\p{L}+)*$

 

 

 

 

 

the devanagari fails

 

 

Edited December 13, 2022 by Attila Kovacs

[Timothy.Prinsloo 0]

@Attila Kovacs just out of interest does work in Delphi... I know it works for C# but isn't the regex syntax different between the two languages

\p{L}+([-+.']\p{L}+)*@\p{L}+([-.]\p{L}+)*\.\p{L}+([-.]\p{L}+)*$ 

 

[Attila Kovacs 629]

44 minutes ago, Timothy.Prinsloo said:

out of interest

there is a PCRE regex in newer Delphi releases, yes, at some degree it will work

[Sherlock 663]

Given the complexity and the tendency of developers to always suggest some totally different approach , here is my completely different suggestion. You seem to have the need to validate an e-mail address before storing it. How about sending a test mail before doing that. That way you get to birds with one stone: Verify the address, and get the permission to use it... a must have in Europe.

[Lajos Juhász 293]

10 minutes ago, Sherlock said:

Given the complexity and the tendency of developers to always suggest some totally different approach , here is my completely different suggestion. You seem to have the need to validate an e-mail address before storing it. How about sending a test mail before doing that. That way you get to birds with one stone: Verify the address, and get the permission to use it... a must have in Europe.

This is an excellent suggestion. I doubt it is a must in Europe, I still receive sensitive information for other people in my e-mail account. 

[Attila Kovacs 629]

20 minutes ago, Sherlock said:

How about sending a test mail before doing that

It's a very-very bad suggestion. You should read an article how not to get into a spam db. First, you have to avoid sending emails to malformed email addresses.

 

20 minutes ago, Sherlock said:

a must have in Europe

Nope. Also, there is a difference between private/non ~ emails, first / second+ contact, etc....

 

 

[Fr0sT.Brutal 900]

I'd rather ask myself WHY I need such validation. Email "rubba@hubba.bubba" will pass any checks but won't gain any sense.

Domain check? They're multiplying like rabbits so you'll have to keep regex up to date + it won't save from "rubba@hubba.com" emails.

 

[Attila Kovacs 629]

3 minutes ago, Fr0sT.Brutal said:

I'd rather ask myself WHY I need such validation

I have it for two reasons, first, ppls. manual input is messy, second, if they copy-paste from websites it can be a strange thing in the edit field and they don't look.

[Fr0sT.Brutal 900]

4 minutes ago, Attila Kovacs said:

I have it for two reasons, first, ppls. manual input is messy, second, if they copy-paste from websites it can be a strange thing in the edit field and they don't look.

For these purposes simple NonSpace{1,}@NonSpace{1,}.NonSpace{2,} will be enough IMHO

[Attila Kovacs 629]

23 minutes ago, Fr0sT.Brutal said:

For these purposes simple NonSpace{1,}@NonSpace{1,}.NonSpace{2,} will be enough IMHO

Yup.

[Timothy.Prinsloo 0]

@Attila Kovacs & @Lars Fosdal Thanks for all the help. I went with this as my solution

 EMAIL_REGEX = '^((((?>[a-zA-Z\d!#$%&’“”''*+\-\/=?^_`{|}~]+\x20*|"((?=[\x01-\x7f])'
               +'[^"\\]|\\[\x01-\x7f])*"\x20*)*(?<angle><))?((?!\.)'
               +'(?>\.?[a-zA-Z\d!#$%&’“”''*+\-\/=?^_`{|}~]+)+|"((?=[\x01-\x7f])'
               +'[^"\\]|\\[\x01-\x7f])*")@(((?!-)[a-zA-Z\d\-]+(?<!-)\.)+[a-zA-Z]{2,}|(((?(?<!)\.)'
               +'(25[0-5]|2[0-4]\d|[01]?\d?\d)){4}|[a-zA-Z\d\-]*[a-zA-Z\d]:((?=[\x01-\x7f])'
               +'[^\\\[\]]|\\[\x01-\x7f])+)\])(?(angle)>))(;\S)*)+$|'
               +'(\p{L}+([-+.]\p{L}+)*@\p{L}+([-.]\p{L}+)*\.\p{L}+([-.]\p{L}+)*$)';

[dummzeuch 1505]

Does that validate Thomas.Müller-Lüdenscheid+privat@abslutseriös.de ? And also the Punycode version of it?

[Sherlock 663]

On 12/14/2022 at 11:44 AM, Attila Kovacs said:

First, you have to avoid sending emails to malformed email addresses.

I would have put that check into an SMTP server. And...surprisingly the good ones do that.