Email validation doesn't work - javascript

I have this simple regular expression for Emails.
/^[a-z]+([\.-_]?[a-z0-9]+)*#([a-z]{3,})+(\.[a-z]{2,3})+$/i;
But when I use this example: first#last#example.com it's still works, And Also when I remove # character from expression :
`/^[a-z]+([\.-_]?[a-z0-9]+)*([a-z]{3,})+(\.[a-z]{2,3})+$/i
it gives the same result.
This expression allows an infinite number of at signs (i.e. #) between at least 2 characters in the email !!
Where is the problem with this expression?

Your pattern is rather restrictive, you might think of other options of validating an email address, like type="email" if it is an input field validation.
As to why the regex matches # even if you take it out, or matches a string with two # symbols, that is cased by [.-_] that matches a lot of chars as the hyphen creates a range that includes #. You need to use [._-] instead.
You may "fix" the regex as
/^[a-z]+([._-]?[a-z0-9]+)*[a-z]{3,}(\.[a-z]{2,3})+$/i
However, this regex is not good to use in real life scenarios.

You want something like that?
/^[a-z\.\-_]+#([a-z]{3,})+(\.[a-z]{2,3})+$/
Probably with sign \.-_ you wanted to have either ".", or "-" or "_" to be used inside the regex, but you forgot to escape "minus".
Or you can use your own but with escape:
^[a-z]+([\.\-_]?[a-z0-9]+)*#([a-z]{3,})+(\.[a-z]{2,3})+$
PS: Remember that a real valid email address could be completely different and has a huge regex, and moreover, each web server defines what is allowed and what is not in email.

Related

validate username with regex in javascript

I am a newbie to regex and would like to create a regular expression to check usernames. These are the conditions:
username must have between 4 and 20 characters
username must not contain anything but letters a-z, digits 0-9 and special characters -._
the special characters -._ must not be used successively in order to avoid confusion
the username must not contain whitespaces
Examples
any.user.13 => valid
any..user13 => invalid (two dots successively)
anyuser => valid
any => invalid (too short)
anyuserthathasasupersuperlonglongname => invalid (too many characters)
any username => invalid because of the whitespace
I've tried to create my own regex and only got to the point where I specify the allowed characters:
[a-z0-9.-_]{4,20}
Unfortunately, it still matches a string if there's a whitespace in between and it's possible to have two special chars .-_ successively:
If anybody would be able to provide me with help on this issue, I would be extremely grateful. Please keep in mind that I'm a newbie on regex and still learning it. Therefore, an explanation of your regex would be great.
Thanks in advance :)
Sometimes writing a regular expression can be almost as challenging as finding a user name. But here you were quite close to make it work. I can point out three reasons why your attempt fails.
First of all, we need to match all of the input string, not just a part of it, because we don't want to ignore things like white spaces and other characters that appear in the input. For that, one will typically use the anchors ^ (match start) and $ (match end) respectively.
Another point is that we need to prevent two special characters to appear next to each other. This is best done with a negative lookahead.
Finally, I can see that the tool you are using to test your regex is adding the flags gmi, which is not what we want. Particularly, the i flag says that the regex should be case insensitive, so it should match capital letters like small ones. Remove that flag.
The final regex looks like this:
/^([a-z0-9]|[-._](?![-._])){4,20}$/
There is nothing really cryptic here, except maybe for the group [-._](?![-._]) which means any of -._ not followed by any of -._.

Javascript - String.search() return true if string contains any characters NOT matching regex

I'm trying to do a search for a character in a string NOT matching the regex :
password.search(/[`!###$%^&*A-Za-z0-9]/i));.
Basically, all characters that aren't this regex isn't allowed and I want to know if the user has input any characters that isn't allowed. For example, '\', or any other characters that I might not think of.
I'm pretty sure there's a question similar to this out somewhere, but despite trying to look for it I surprisingly couldn't find it. If this is a duplicate question please link me.
According to this answer, you could use ?!:
console.log("valid$\\".search(/(?![`!###$%^&*A-Za-z0-9])/i));
console.log("256)128".search(/(?![`!###$%^&*A-Za-z0-9])/i));
f you want to exclude a set of characters (some punctuation characters, for example) you would use the ^ operator at the beginning of a character set, in a regex .

Simple regex pattern for email

I've been trying to work this out for almost an hour now, and I can't see myself getting much further with it without any help or explanation. I've used regex before, but only ones that are very simple or had already been made.
This time, I'm trying to work out how to write a regex that achieves the following:
Email address must contain one # character and at least one dot (.) at least one position after the # character.
So far, this is all I've been able to work out, and it still matches email addresses that, for example, have more than one # symbol.
.*?#?[^#]*\.+.*
It would be helpful if you can show me how to construct a regular expression that checks for a single # and at least one full stop one or more spaces after the #. If you could break down the regex and explain what each bit does, that would be really helpful.
I want to keep it simple for now, so it doesn't have to be a full-on super-accurate email validation expression.
With the help of ClasG's comment, I now have a fairly straightforward and suitable regex for my problem. For the sake of anyone learning regex who might come across this question in the future, I'll break the expression down below.
Expression: ^[^#]+#[^#]+\.[^#]+$
^ Matches the beginning of the string (or line if multiline)
[^#] Match any character that is not in this set (i.e. not "#")
+ Match one or more of this
# Match "#" character
[^#] Match any character that is not in this set
+ Match one or more
\. Match "." (full stop) character (backslash escapes the full stop)
[^#] Match any character that is not in this set
+ Match one or more
$ Matches the end of the string (or line if multiline)
And in plain language:
Start at beginning of string or line
Include all characters except # until the # sign
Include the # sign
Include all characters except # after the # sign until the full stop
Include all characters except # after the full stop
Stop at the end of the string or line
Email address must contain one # character
No they don't. An email address with no '#' character is perfectly valid. An email address with multiple '#' characters before an IP address is perfectly valid (as long as all but 1 are outside the ADDR_SPEC or are quoted/escaped within the mailbox name).
I suspect you're not trying to validate an email address but rather an ADDR_SPEC. The answer linked by Máté Safranka describes how to validate an ADDR_SPEC (not an email address). Unless you expect to be validating records which don't have a valid internet MX record, and more than one '#' is more likely be a typo than a valid address....
/[a-z0-9\._%+!$&*=^|~#%'`?{}/\-]+#([a-z0-9\-]+\.){1,}([a-z]{2,16})/
^[^\W_]+\w*(?:[.-]\w*)*[^\W_]+#[^\W_]+(?:[.-]?\w*[^\W_]+)*(?:\.[^\W_]{2,})$

Validate email with RegEx following rules

Needs to only contain [a-zA-Z0-9.], and followed by an # then the same match afterward, the match before, and after the # shouldn't be any longer than 64 characters long, and at least one length.
^([a-zA-Z0-9\-\.]+){1,64}#([a-zA-Z0-9\-\.]){1,64}$
This seems to work but it sometimes takes forever, why is this?
I'm not sure why you have the + operator in the first part of the regex. I hope this could be useful for you
^([a-zA-Z\d\.]{1,64})#([a-zA-Z\d\.]{1,64})$
For email regex you should use http://emailregex.com/ which provides this regex
/^(([^<>()\[\]\\.,;:\s#"]+(\.[^<>()\[\]\\.,;:\s#"]+)*)|(".+"))#((\[[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,}))$/
also, if you can you should usually just use
<input type="email">

Find e-mails on string

I asked this question a few days ago:
Unable to get a specific value on a JSON object
The first answer was just perfect. Now I need to modify that regular expression in order to find e-mails. The problem is I don't know anything about regular expressions and I've been looking around but don't seem to be able to pull it off.
This is the code:
var m=null
, result=JSON.stringify(response)
, re=/"message":"([^"]+)"/g
, messages=[];
while( m=re.exec(result) ) {
messages.push(m[1]);
Everything is explained on my other question, but basically what this code does is get message":"THIS TEXT"
Now I want to find out whether that text contains an e-mail or not.
I've been checking out many javascript regexp examples and find it rather confusing so if you could give me a little explanation (or something to read) about why it's done the way it's done I'd really appreciate it.
Regexp you are looking for is long and ugly. The email address definition in RFC standard is too sophisticated and permissive. See "Valid email addresses" section on wikipedia. But, you can check whether string looks like email with this simple regexp:
/^.+#.+\..+$/
The explanation of how this works can be found at Regexper
There are some very, very long regexes that you can use to validate emails based on RFC standards. Here is a regex that verifies regexes based on RFC882, which is anything from short and easy-to-understand.
If you wanted to validate anything that looked like an email, you could use this:
^.+#.+\..+$
But, this regex will also allow spaces, and multiple # symbols. So, you could use this:
^[^#]+#[^#]+\.[^#]+$
But this will allow special characters in the name and TLD, so, here's a short regex that will match almost all English emails (as well as those that aren't english):
^([a-zA-Z0-9\-_\~\!\$\&\'\(\)\*\+\,;\:\=]+)\#(.+)\.([a-zA-Z]{2,36})$
This regex will match the characters a-z, A-Z, 0-9, -, _, ~, !, $, &, ', (, ), *, +, ,, ;, :, and = one or more times before the # symbol, will match any characters after the # symbol (almost all characters are now allowed with the new international domains), and allows a-z or A-Z 2 or more times as the TLD.
There are some international domains that do not have english characters in them, so it may be best to replace [a-zA-Z]{2,36} with .{2,36}, if you're expecting and international audience.
Here's a live preview of Regex #1 on regex101.com.
Here's a live preview of Regex #2 on regex101.com.
Here's a live preview of Regex #3 on regex101.com.

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