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php – Allow + in regex email validate email

Posted by: admin July 12, 2020 Leave a comment

Questions:

Regex is blowing my mind. How can I change this to validate emails with a plus sign? so I can sign up with [email protected]

if(!preg_match("/^[_a-z0-9-]+(\.[_a-z0-9-]+)*@[a-z0-9-]+(\.[a-z0-9-]+)*$/i", $_GET['em'])) {
How to&Answers:

It seems like you aren’t really familiar with what your regex is doing currently, which would be a good first step before modifying it. Let’s walk through your regex using the email address [email protected] (in each section below, the bolded part is what is matched by that section):

  1. ^ is the start of string
    anchor
    .
    It specifies that any match must
    begin at the beginning of the
    string. If the pattern is not
    anchored, the regex engine can match
    a substring, which is often
    undesired.

    Anchors are zero-width, meaning that
    they do not capture any characters.

  2. [_a-z0-9-]+ is made up of two
    elements, a character
    class

    and a repetition
    modifer
    :

    • [...] defines a character class, which tells the regex engine,
      any of these characters are valid matches. In this case the class
      contains the characters a-z, numbers
      0-9 and the dash and underscore (in
      general, a dash in a character class
      defines a range, so you can use
      a-z instead of
      abcdefghijklmnopqrstuvwxyz; when
      given as the last character in the
      class, it acts as a literal dash).
    • + is a repetition modifier that specifies that the preceding token
      (in this case, the character class)
      can be repeated one or more times.
      There are two other repetition
      operators: * matches zero or more
      times; ? matches exactly zero or
      one times (ie. makes something
      optional).

    (captures
    john[email protected])

  3. (\.[_a-z0-9-]+)* again contains a
    repeated character class. It also
    contains a
    group,
    and an escaped character:

    • (...) defines a group, which allows you to group multiple tokens
      together (in this case, the group
      will be repeated as a
      whole).
      Let’s say we wanted to
      match ‘abc’, zero or more times (ie.
      abcabcabc matches, abcccc doesn’t).
      If we tried to use the pattern
      abc*, the repetition modifier
      would only apply to the c, because
      c is the last token before the
      modifier. In order to get around
      this, we can group abc ((abc)*),
      in which case the modifier would
      apply to the entire group, as if it
      was a single token.
    • \. specifies a literal dot character. The reason this is needed
      is because . is a special
      character in regex, meaning any
      character
      .
      Since we want to match an actual dot
      character, we need to escape it.

    (captures
    john.robert.smith@mail.com)

  4. @ is not a special character in
    regex, so, like all other
    non-special characters, it matches
    literally.

    (captures john.robert.smith@mail.com)

  5. [a-z0-9-]+ again defines a repeated character class, like item #2 above.

    (captures [email protected]mail.com)

  6. (\.[a-z0-9-]+)* is almost exactly the same pattern as #3 above.

    (captures [email protected].com)

  7. $ is the end of string anchor. It works the same as ^ above, except matches the end of the string.


With that in mind, it should be a bit clearer how to add a section with captures a plus segment. As we saw above, + is a special character so it has to be escaped. Then, since the + has to be followed by some characters, we can define a character class with the characters we want to match and define its repetition. Finally, we should make the whole group optional because email addresses don’t need to have a + segment:

(\+[a-z0-9-]+)?

When inserted into your regex, it’d look like this:

/^[_a-z0-9-]+(\.[_a-z0-9-]+)*(\+[a-z0-9-]+)[email protected][a-z0-9-]+(\.[a-z0-9-]+)*$/i

Answer:

Save your sanity. Get a pre-made PHP RFC 822 Email address parser

Answer:

I’ve used this regex to validate emails, and it works just fine with emails that contain a+:

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

Answer:

\+ will match a literal + sign, but be aware: You still won’t be close to matching all possible email addresses according to the RFC spec, because the actual regex for that is madness. It’s almost certainly not worth it; you should use a real email parser for this.

Answer:

This is another solution (is similar to the solution found by David):

//Escaped for .Net
^[_a-zA-Z0-9-]+((\.[_a-zA-Z0-9-]+)*|(\+[_a-zA-Z0-9-]+)*)*@[a-zA-Z0-9-]+(\.[a-zA-Z0-9-]+)*(\.[a-zA-Z]{2,4})$

//Native
^[_a-zA-Z0-9-]+((\.[_a-zA-Z0-9-]+)*|(\+[_a-zA-Z0-9-]+)*)*@[a-zA-Z0-9-]+(\.[a-zA-Z0-9-]+)*(\.[a-zA-Z]{2,4})$

Answer:

This is the another solution

/^[_a-z0-9-+]+(\.[_a-z0-9-+]+)*(\+[a-z0-9-]+)[email protected][a-z0-9-.]+(\.[a-z0-9]+)$/

or For razor page(@=\u0040)

/^[_a-z0-9-+]+(\.[_a-z0-9-+]+)*(\+[a-z0-9-]+)?\u0040[a-z0-9-.]+(\.[a-z0-9]+)$/