Question

I have a RegEx here and I need to know if it will 100% omit any bad email addresses but I do not understand them fully so need to call on the community experts.

The string is as follows:

^[_a-zA-Z0-9-]+(.[_a-zA-Z0-9-]+)*@[a-zA-Z0-9-]+(.[a-zA-Z0-9-]+)*(.[a-zA-Z]{2,3})$

Thank you in advance!

Answer 1

^[_a-zA-Z0-9-]+(.[_a-zA-Z0-9-]+)*@[a-zA-Z0-9-]+(.[a-zA-Z0-9-]+)*(.[a-zA-Z]{2,3})$

Piece by piece

    ^  Start of the string

    [_a-zA-Z0-9-]+ One or more characters of "_" (no quotes), a letter (a-z, A-Z), a number (0-9), or "-" (no quotes)
    (.[_a-zA-Z0-9-]+)* zero or more substrings of type .something, or .123, or .a123. The substring must be formed by a . and a letter (same group of letters as before). So "." is not valid. ".a" or ".1" or ".-" is.

(up until now it will accept for example my.name12 or my.name12.surname34)

    @ a "@" (like max@something)

    [a-zA-Z0-9-]+ One or more characters with the same pattern as before
    (.[a-zA-Z0-9-]+)* Zero or more substrings of type ".something"... just as before
    (.[a-zA-Z]{2,3}) A "." (dot) and 2 or 3 letters (a-z or A-Z)

    $ The end of the string

So we have an email address, where you can’t have [e-mail] (no “dangling” dot before the @) or [e-mail] (no beginning dot). The domain must start with a letter and can’t have a dot just before the first level domain (.com/.uk/??), so no something@x..com. The first-level domain must have 2 or 3 letters (no numbers)

There is an error, the . (dot) must be escaped, so it should be \. . Depending on the language, the \ must be escaped in a string (so it could be \\.)