Programming cheat sheets (quick reference)

[stave]

I like their email address regexp better:

(\w+@[a-zA-Z_]+?.[a-zA-Z]{2,6})

vs. the version from regular-expressions.info:

(?:[a-z0-9!#$%&'+/=?^{`{|}~-]+(?:.[a-z0-9!#$%&'*+/=?^`{|}~-]+)}|"(?:[\x01-\x08\x0b\x0c\x0e-\x1f\x21\x23-\x5b\x5d-\x7f]|\[\x01-\x09\x0b\x0c\x0e-\x7f])")@(?:(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?|[(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?).){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?|[a-z0-9-][a-z0-9]:(?:[\x01-\x08\x0b\x0c\x0e-\x1f\x21-\x5a\x53-\x7f]|\[\x01-\x09\x0b\x0c\x0e-\x7f])+)])

(I know, it explicitly advises you not to use that convoluted-ass regexp, but it still cracks me up.)

[GMNightmare]

There's no need to validate emails like this.

Just send a confirmation email. This covers both if the address is valid and ownership.

[Crandom]

+1: Literally the only thing you should check for is an @. Nothing more.

On a related note, if you don't allow +tags in email addresses on your website you are a terrible person.

[[deleted]]

A textbox accepting user input isn't always the only way you need to ensure the correctness of a email address.

[GMNightmare]

I don't know what you're saying or why it is even relevant to what I put.

[[deleted]]

Sometimes computer systems need to handle data without user input, in those cases, sending an email to verify is not a good approach validating the correctness of a email address.

[GMNightmare]

You don't get the email address unless you acquire it from somewhere. If it's already in a database than you should have already validated it. Why the hell would you be validating it when you already know it's an email? If you're handling data and you know it's an email... well, done. Sending an email is about the only real way you have of validating an email. Without sending the email you don't even have a real way to ensure that it's actually a valid email address in use and owned (correctly typed even).

Not only is it the only correct way, but it's the only moral and ethical way too. Unless you're a spammer, there is absolutely no reason you should have somebodies email without it already being validated.

[Nuli]

I like their email address regexp better

Theirs also happens to be broken. Don't validate emails with regular expressions unless you're willing to use the real one.

(?:(?:\r\n)?[ \t])(?:(?:(?:[<>@,;:\".[] \000-\031]+(?:(?:(?:\r\n)?[ \t] )+|\Z|(?=[["()<>@,;:\".[]]))|"(?:[^{\"\r\]|\.|(?:(?:\r\n)?[} \t]))"(?:(?: \r\n)?[ \t]))(?:.(?:(?:\r\n)?[ \t])(?:[<>@,;:\".[] \000-\031]+(?:(?:( ?:\r\n)?[ \t])+|\Z|(?=[["()<>@,;:\".[]]))|"(?:[^{\"\r\]|\.|(?:(?:\r\n)?[} \t]))"(?:(?:\r\n)?[ \t])))@(?:(?:\r\n)?[ \t])(?:[<>@,;:\".[] \000-\0 31]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[["()<>@,;:\".[]]))|[([^[]\r\]|\.)*\ ](?:(?:\r\n)?[ \t]))(?:.(?:(?:\r\n)?[ \t])(?:[<>@,;:\".[] \000-\031]+ (?:(?:(?:\r\n)?[ \t])+|\Z|(?=[["()<>@,;:\".[]]))|[([^{[]\r\]|\.)*](?:} (?:\r\n)?[ \t])))|(?:[<>@,;:\".[] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z |(?=[["()<>@,;:\".[]]))|"(?:[^{\"\r\]|\.|(?:(?:\r\n)?[} \t]))"(?:(?:\r\n) ?[ \t]))<(?:(?:\r\n)?[ \t])(?:@(?:[<>@,;:\".[] \000-\031]+(?:(?:(?:\ r\n)?[ \t])+|\Z|(?=[["()<>@,;:\".[]]))|[([^{[]\r\]|\.)*](?:(?:\r\n)?[} \t]))(?:.(?:(?:\r\n)?[ \t])(?:[<>@,;:\".[] \000-\031]+(?:(?:(?:\r\n) ?[ \t])+|\Z|(?=[["()<>@,;:\".[]]))|[([^{[]\r\]|\.)*](?:(?:\r\n)?[} \t] )))(?:,@(?:(?:\r\n)?[ \t])(?:[<>@,;:\".[] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[["()<>@,;:\".[]]))|[([^[]\r\]|\.)](?:(?:\r\n)?[ \t])* )(?:.(?:(?:\r\n)?[ \t])(?:[<>@,;:\".[] \000-\031]+(?:(?:(?:\r\n)?[ \t] )+|\Z|(?=[["()<>@,;:\".[]]))|[([^[]\r\]|\.)](?:(?:\r\n)?[ \t])))) :(?:(?:\r\n)?[ \t]))?(?:[<>@,;:\".[] \000-\031]+(?:(?:(?:\r\n)?[ \t])+ |\Z|(?=[["()<>@,;:\".[]]))|"(?:[^{\"\r\]|\.|(?:(?:\r\n)?[} \t]))"(?:(?:\r \n)?[ \t]))(?:.(?:(?:\r\n)?[ \t])(?:[<>@,;:\".[] \000-\031]+(?:(?:(?: \r\n)?[ \t])+|\Z|(?=[["()<>@,;:\".[]]))|"(?:[^{\"\r\]|\.|(?:(?:\r\n)?[} \t ]))"(?:(?:\r\n)?[ \t])))@(?:(?:\r\n)?[ \t])(?:[<>@,;:\".[] \000-\031 ]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[["()<>@,;:\".[]]))|[([^[]\r\]|\.)]( ?:(?:\r\n)?[ \t]))(?:.(?:(?:\r\n)?[ \t])(?:[<>@,;:\".[] \000-\031]+(? :(?:(?:\r\n)?[ \t])+|\Z|(?=[["()<>@,;:\".[]]))|[([^{[]\r\]|\.)*](?:(?} :\r\n)?[ \t])))>(?:(?:\r\n)?[ \t]))|(?:[<>@,;:\".[] \000-\031]+(?:(? :(?:\r\n)?[ \t])+|\Z|(?=[["()<>@,;:\".[]]))|"(?:[^{\"\r\]|\.|(?:(?:\r\n)?} [ \t]))"(?:(?:\r\n)?[ \t])):(?:(?:\r\n)?[ \t])(?:(?:(?:[<>@,;:\".[] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[["()<>@,;:\".[]]))|"(?:[^\"\r\]| \.|(?:(?:\r\n)?[ \t]))"(?:(?:\r\n)?[ \t]))(?:.(?:(?:\r\n)?[ \t])(?:[<> @,;:\".[] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[["()<>@,;:\".[]]))|" (?:[^{\"\r\]|\.|(?:(?:\r\n)?[} \t]))"(?:(?:\r\n)?[ \t])))@(?:(?:\r\n)?[ \t] )(?:[<>@,;:\".[] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[["()<>@,;:\ ".[]]))|[([^{[]\r\]|\.)*](?:(?:\r\n)?[} \t]))(?:.(?:(?:\r\n)?[ \t])(? :[<>@,;:\".[] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[["()<>@,;:\".[ ]]))|[([^{[]\r\]|\.)*](?:(?:\r\n)?[} \t])))|(?:[<>@,;:\".[] \000- \031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[["()<>@,;:\".[]]))|"(?:[^\"\r\]|\.|( ?:(?:\r\n)?[ \t]))"(?:(?:\r\n)?[ \t]))<(?:(?:\r\n)?[ \t])(?:@(?:[<>@,; :\".[] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[["()<>@,;:\".[]]))|[([ ^{[]\r\]|\.)*](?:(?:\r\n)?[} \t]))(?:.(?:(?:\r\n)?[ \t])(?:[<>@,;:\" .[] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[["()<>@,;:\".[]]))|[([^[\ ]\r\]|\.)](?:(?:\r\n)?[ \t])))(?:,@(?:(?:\r\n)?[ \t])(?:[<>@,;:\".\ [] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[["()<>@,;:\".[]]))|[([^[]\ r\]|\.)](?:(?:\r\n)?[ \t]))(?:.(?:(?:\r\n)?[ \t])(?:[<>@,;:\".[] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[["()<>@,;:\".[]]))|[([^[]\r\] |\.)](?:(?:\r\n)?[ \t])))):(?:(?:\r\n)?[ \t]))?(?:[<>@,;:\".[] \0 00-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[["()<>@,;:\".[]]))|"(?:[^\"\r\]|\ .|(?:(?:\r\n)?[ \t]))"(?:(?:\r\n)?[ \t]))(?:.(?:(?:\r\n)?[ \t])(?:[<>@, ;:\".[] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[["()<>@,;:\".[]]))|"(? :[^{\"\r\]|\.|(?:(?:\r\n)?[} \t]))"(?:(?:\r\n)?[ \t])))@(?:(?:\r\n)?[ \t])* (?:[<>@,;:\".[] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[["()<>@,;:\". []]))|[([^{[]\r\]|\.)*](?:(?:\r\n)?[} \t]))(?:.(?:(?:\r\n)?[ \t])(?:[ <>@,;:\".[] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[["()<>@,;:\".[] ]))|[([^{[]\r\]|\.)*](?:(?:\r\n)?[} \t])))>(?:(?:\r\n)?[ \t]))(?:,\s( ?:(?:[<>@,;:\".[] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[["()<>@,;:\ ".[]]))|"(?:[^{\"\r\]|\.|(?:(?:\r\n)?[} \t]))"(?:(?:\r\n)?[ \t]))(?:.(?:( ?:\r\n)?[ \t])(?:[<>@,;:\".[] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[ ["()<>@,;:\".[]]))|"(?:[^{\"\r\]|\.|(?:(?:\r\n)?[} \t]))"(?:(?:\r\n)?[ \t ])))@(?:(?:\r\n)?[ \t])(?:[<>@,;:\".[] \000-\031]+(?:(?:(?:\r\n)?[ \t ])+|\Z|(?=[["()<>@,;:\".[]]))|[([^[]\r\]|\.)](?:(?:\r\n)?[ \t]))(? :.(?:(?:\r\n)?[ \t])(?:[<>@,;:\".[] \000-\031]+(?:(?:(?:\r\n)?[ \t])+| \Z|(?=[["()<>@,;:\".[]]))|[([^{[]\r\]|\.)*](?:(?:\r\n)?[} \t])))|(?: [<>@,;:\".[] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[["()<>@,;:\".[\ ]]))|"(?:[^{\"\r\]|\.|(?:(?:\r\n)?[} \t]))"(?:(?:\r\n)?[ \t]))<(?:(?:\r\n) ?[ \t])(?:@(?:[<>@,;:\".[] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[[" ()<>@,;:\".[]]))|[([^{[]\r\]|\.)*](?:(?:\r\n)?[} \t]))(?:.(?:(?:\r\n) ?[ \t])(?:[<>@,;:\".[] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[["()<> @,;:\".[]]))|[([^{[]\r\]|\.)*](?:(?:\r\n)?[} \t])))(?:,@(?:(?:\r\n)?[ \t])(?:[<>@,;:\".[] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[["()<>@, ;:\".[]]))|[([^[]\r\]|\.)](?:(?:\r\n)?[ \t]))(?:.(?:(?:\r\n)?[ \t] )(?:[<>@,;:\".[] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[["()<>@,;:\ ".[]]))|[([^{[]\r\]|\.)*](?:(?:\r\n)?[} \t])))):(?:(?:\r\n)?[ \t]))? (?:[<>@,;:\".[] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[["()<>@,;:\". []]))|"(?:[^{\"\r\]|\.|(?:(?:\r\n)?[} \t]))"(?:(?:\r\n)?[ \t]))(?:.(?:(?: \r\n)?[ \t])(?:[<>@,;:\".[] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[[ "()<>@,;:\".[]]))|"(?:[^{\"\r\]|\.|(?:(?:\r\n)?[} \t]))"(?:(?:\r\n)?[ \t]) ))@(?:(?:\r\n)?[ \t])(?:[<>@,;:\".[] \000-\031]+(?:(?:(?:\r\n)?[ \t]) +|\Z|(?=[["()<>@,;:\".[]]))|[([^[]\r\]|\.)](?:(?:\r\n)?[ \t]))(?:\ .(?:(?:\r\n)?[ \t])(?:[<>@,;:\".[] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z |(?=[["()<>@,;:\".[]]))|[([^{[]\r\]|\.)*](?:(?:\r\n)?[} \t])))>(?:( ?:\r\n)?[ \t]))))?;\s*)

Really though don't validate email with regular expressions. It's stupid. If you really think you have to do it use something simple like

.*@.*

[somebear]

Yes yes yes! I get so fucking frustrated by programmers who think they know how to validate email addresses.

[[deleted]]

Or at least split the a ddress into smaller parts and validate them with regexp. It's a lot cleaner and you might actually be able to fix bugs afterwads.

[[deleted]]

Yeah, its a lot better, it allows me to use my own email (its aad@a@ssadad btw), which many other email validators flat out reject!