[SOLVED] Help Understanding Validation

[bassguru]

Hello everyone,

 

I am currently using an email validater for my site. But I need some help understanding how it works...

 

$regexp="^[_a-z0-9-]+(\.[_a-z0-9-]+)*@[a-z0-9-]+(\.[a-z0-9-]+)*(\.[a-z]{2,3})^";

 

The code works, but I just don't understand some of the components to the code! Could someone please explain to me how it works?

 

Many thanks

Bassguru

[JonnoTheDev]

A complete explanation provided by regexbuddy (get this program, it is golddust). You can see there are errors in the pattern.

^[_a-z0-9-]+(\.[_a-z0-9-]+)*@[a-z0-9-]+(\.[a-z0-9-]+)*(\.[a-z]{2,3})^

Assert position at the start of the string «^»
Match a single character present in the list below «[_a-z0-9-]+»
   Between one and unlimited times, as many times as possible, giving back as needed (greedy) «+»
   The character "_" «_»
   A character in the range between "a" and "z" «a-z»
   A character in the range between "0" and "9" «0-9»
   The character "-" «-»
Match the regular expression below and capture its match into backreference number 1 «(\.[_a-z0-9-]+)*»
   Between zero and unlimited times, as many times as possible, giving back as needed (greedy) «*»
   Note: You repeated the backreference itself.  The backreference will capture only the last iteration.  Put the backreference inside a group and repeat that group to capture all iterations. «*»
   Match the character "." literally «\.»
   Match a single character present in the list below «[_a-z0-9-]+»
      Between one and unlimited times, as many times as possible, giving back as needed (greedy) «+»
      The character "_" «_»
      A character in the range between "a" and "z" «a-z»
      A character in the range between "0" and "9" «0-9»
      The character "-" «-»
Match the character "@" literally «@»
Match a single character present in the list below «[a-z0-9-]+»
   Between one and unlimited times, as many times as possible, giving back as needed (greedy) «+»
   A character in the range between "a" and "z" «a-z»
   A character in the range between "0" and "9" «0-9»
   The character "-" «-»
Match the regular expression below and capture its match into backreference number 2 «(\.[a-z0-9-]+)*»
   Between zero and unlimited times, as many times as possible, giving back as needed (greedy) «*»
   Note: You repeated the backreference itself.  The backreference will capture only the last iteration.  Put the backreference inside a group and repeat that group to capture all iterations. «*»
   Match the character "." literally «\.»
   Match a single character present in the list below «[a-z0-9-]+»
      Between one and unlimited times, as many times as possible, giving back as needed (greedy) «+»
      A character in the range between "a" and "z" «a-z»
      A character in the range between "0" and "9" «0-9»
      The character "-" «-»
Match the regular expression below and capture its match into backreference number 3 «(\.[a-z]{2,3})»
   Match the character "." literally «\.»
   Match a single character in the range between "a" and "z" «[a-z]{2,3}»
      Between 2 and 3 times, as many times as possible, giving back as needed (greedy) «{2,3}»
Assert position at the start of the string «^»

[bassguru]

Exactly what I wanted, thanks for the help neil.johnson!

[Psycho]

Nice tip Neil.

 

bassguru,

 

If I may, I think your pattern has some holes. For one, it does not allow the plus sign in the username, which is perfectly valid for an email address. Also, for the TLD you are only accepting 2 or 3 letter values. There are plenty of valid TLDs that are more than 3 characters in length (.MUSEUM and .TRAVEL being the longest ones I know of).

 

Here is the function I use for email validation. It validates the format and the length. Feel free to point out any flaws:

 

//=====================================================
// Function: is_email ( string $email )
//
// Description: Finds whether the given string variable
//              is a properly formatted email.
//
// Parameters: $email the string being evaluated
//
// Return Values: Returns TRUE if $email is valid email
//                format, FALSE otherwise.
//=====================================================

function is_email($email) {

    $formatTest = '/^[-\w+]+(\.[-\w+]+)*@[-a-z\d]{2,}(\.[-a-z\d]{2,})*\.[a-z]{2,6}$/i';
    $lengthTest = '/^(.{1,64})@(.{4,255})$/';

    return (preg_match($formatTest, $email) && preg_match($lengthTest, $email));

}

// NOTES:
//
// Format test
// - Username accepts: 'a-z', 'A-Z', '0-9', '_' (underscore), '-' (dash), '+' (plus), & '.' (period)
//       Note: cannot start or end with a period (and connot be in succession)
// - Domain accepts: 'a-z', 'A-Z', '0-9', '-' (dash), & '.' (period)
//       Note: cannot start or end with a period (and connot be in succession)
// - TLD accepts: 'a-z' & 'A-Z'
//
// Length test
// - Username: 1 to 64 characters
// - Domain: 4 to 255 character