Regular expression for validating email
Google Forms makes it relatively easy to add such advanced date validation rules to individual fields through Regular Expressions (or regex or regexp).Think of them as search patterns and every character entered in a form field is matched against that pattern – the form can only be submitted if the patter and the user-input matches. Say your Google form expects the user to enter their year of birth.So I drop the pattern into the project and start parsing addresses and of them come back as invalid. Certainly when asking around on Twitter there was a lot of ire at the inconsistency of email regexes and as some said, it’s actually not even possible, at least not without excluding various valid patterns. He does go on to point out a very poignant comment in his subsequent post: Now of course that’s very context-sensitive statement too; yes, this would work well at the point of registration on a website but no, it doesn’t work well when you’re parsing hundreds of millions of addresses in a data dump!Stuff like [email protected] and [email protected] get binned and that’s just great. The point of all this is firstly to say “Don’t trust the default validator in the regex control of ASP. It’s a fair assumption to make – that Microsoft will give you a validator that actually works – but it’s an incorrect assumption. My case is special and again, I’ll detail it more later, but my particular priorities are on having a higher degree of confidence in the integrity data I have rather than ensuring obscure edge-case addresses are allowed through.Your organization has a few vacant positions and you are planning to use the Google Forms service to prepare a pre-interview questionnaire for job applicants.You have created a form and it has all the standard fields where candidates can enter their name, email address, website URL, phone number, zip code and other essential details.Secondly, clearly we need something more decent and obviously it’s easy to replace the one in the validator or drop it into your C# as required. Oh – and just in case anyone is interested, here’s a dump of those 3,423 rejected email addresses (alpha chars substituted with “x’ for the sake of anonymity then distilled to a distinct list of 1,905 records).I grabbed Phil’s from the post above which looks like this: Huh? If, for argument’s sake, 10% of those are false positives (and I highly doubt it’s that high), we’re looking at 0.04% of the original dataset being invalid.
Clearly it’s time for a regex because you can fix anything with a regex, right? I thought the easiest way to get this right straight off the bat would be to just grab a regex validator from an ASP.
When you are expecting dozens, or even hundreds, of responses in your Google Forms, it is always a good idea to have some rules in place and respondents data should be matched against these rules even before they submit the form.
For instance, if your form is asking for a person’s year of birth, they should only be allowed to enter a number between 19.
These Regexs are examples and not built for a particular Regex engine. In particular, this means that character classes do not contain meta characters which need to be escaped, except the Regex Library Site A site that has a HUGE library of regular expressions and other regex resources Regex Tutorial Site A site with lots of tutorials on writing Regexs and numerous examples Regex Construction Tool A free regex construction tool Regex Explanation Tool
Email validation using regular expressions is common task which may be required in any application which seek email address as required information in registration step.
NET web forms project and copy the pattern into my project. NET as in the framework itself that has it wrong, rather it’s the default value Visual Studio provides when selecting the expression above) Now you can read the spec and get a headache or you can take a look at Wikipedia’s description of the “local part” of an email address: The third bullet says dashes are good – what gives?! At the end of the day, being too liberal is probably not a bad thing – is it really so bad if someone registers with an invalid address? On the other hand, being too stringent can mean losing a customer which is probably a whole lot worse.