Develop Reference

Validating client-side data input using a pattern

I am currently working on a project whereby data can be added into a database via a website. Currently I have managed to configure it so that the form accepts title, postcode, vehicle reg and ID number.
Javascript validation is working fine for these entries, with the exception of ID number. All ID numbers are a specific format (2 numbers followed by a . followed by 4 numbers).
I cannot seem to work out how to define the pattern.
Due to the size of my code, I have not posted the full code here (all is validating except this ID validation), but I've provided a snip of the 'if' statement below which I'm trying to come up with.
if (inputElement.id == "wid") {
pattern = /^[a-zA-Z0-9 ]*$/;
feedback = "Only 2 numbers followed by a . followed by 4 numbers are
permitted";
I know that the pattern isn't correct here but I have searched for hours trying to locate some easy to explain guidance and cannot find anything which appears to be relevant.
Any thoughts would be appreciated.
Thank you

You can try out something like https://regex101.com/ to test you regexes, and see an explanation of it.
I think your pattern should be this: /^[0-9]{2}\.[0-9]{4}$/.
The first part ([0-9]{2}) makes sure that the id starts with 2 digits, then a dot \. (which must be escaped, because it means "every character" otherwise) and then 4 digits [0-9]{4}

Email Validation RegEx username/local name length check not running

I've debugged for a few hours now and have hit a wall - regex has never been my strongsuit. I have been able to alter the following regex to restrict 255 characters for domain fine, however, in trying to restrict the local/username portion of an email address I'm running into issues implementing a 64 character limit. I've gone through regex101 replacing +s and *s and attempting to understand what each pass is doing - however, even when I add a check against all non-whitespace characters with a limit of 64 it seems like the other checks pass and take precedence - although I'm not sure. Below is my regex currently without any of the 64 character checks that I've broken it with:
var emailCheck = new RegExp(/^((([a-z]|\d|[!#\$%&'\*\+\-\/=\?\^_`{\|}~]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])+(\.{0,1}([a-z]|\d|[!#\$%&'\*\+\-\/=\?\^_`{\|}~]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])+)*)|((\x22)((((\x20|\x09)*(\x0d\x0a))?(\x20|\x09)+)?(([\x01-\x08\x0b\x0c\x0e-\x1f\x7f]|\x21|[\x23-\x5b]|[\x5d-\x7e]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])|(\\([\x01-\x09\x0b\x0c\x0d-\x7f]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF]))))*(((\x20|\x09)*(\x0d\x0a))?(\x20|\x09)+)?(\x22)))#((([a-z]|\d|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])|(([a-z]|\d|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])([a-z]|\d|-|\.|_|~|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF]){1,255}([a-z]|\d|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])))\.)+(([a-z]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])|(([a-z]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])([a-z]|\d|-|\.|_|~|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF]){1,255}([a-z]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])))\.*$/i);
What I have so far can be seen at http://jsfiddle.net/mtqx0tz1/ , I've made other slight alterations (e.g. not allowing consecutive dots) but for the most part this regex comes from another stack post without the character limits.
Lastly, I'm aware this isn't the 'standard' so to speak and emails are checked server-side, however, I would like to be more safe than sorry...as well as work on some of my regex. Sorry if this question isn't worthy of an actual post - I'm just simply not seeing where in my passes {1,64} is failing. At this point I'm thinking about just sub-stringing the portion of the string up to the # sign and checking length that way...but it would be nice to include it in this statement since all the checks are done here to begin with.

I have used this regex validation and it works good.
The e-mail address is in the variable strIn
try
{
return Regex.IsMatch(strIn,
#"^(?("")("".+?(?<!\\)""#)|(([0-9a-z]((\.(?!\.))|[-!#\$%&'\*\+/=\?\^`\{\}\|~\w])*)(?<=[0-9a-z])#))" +
#"(?(\[)(\[(\d{1,3}\.){3}\d{1,3}\])|(([0-9a-z][-\w]*[0-9a-z]*\.)+[a-z0-9][\-a-z0-9]{0,22}[a-z0-9]))$",
RegexOptions.IgnoreCase, TimeSpan.FromMilliseconds(250));
}
catch (RegexMatchTimeoutException)
{
return false;
}

Performance issue while evaluating email address with a regular expression

I am using below regular expression to validate email address.
/^\w+([\.-]?\w+)*#\w+([\.-]?w+)*(\.\w{2,3})+$/
Javascript Code:
var email = 'myname#company.com';
var pattern = /^\w+([\.-]?\w+)*#\w+([\.-]?w+)*(\.\w{2,3})+$/;
if(pattern.test(email)){
return true;
}
The regex evaluates quickly when I provide the below invalid email:
aseflj#$kajsdfklasjdfklasjdfklasdfjklasdjfaklsdfjaklsdjfaklsfaksdjfkasdasdklfjaskldfjjdkfaklsdfjlak#company.com
(I added #$ in the middle of the name)
However when I try to evaluate this email it takes too much time and the browser hangs.
asefljkajsdfklasjdfklasjdfklasdfjklasdjfaklsdfjaklsdjfaklsfaksdjfkasdasdklfjaskldfjjdkfaklsdfjlak#company.com1
(I added com1 in the end)
I'm sure that the regex is correct but not sure why its taking so much time to evaluate the second example. If I provide an email with shorter length it evaluates quickly. See the below example
dfjjdkfaklsdfjlak#company.com1
Please help me fix the performance issue

Your regex runs into catastrophic backtracking. Since [\.-]? in ([\.-]?\w+)* is optional, it makes the group degenerates to (\w+)*, which is a classic case of catastrophic backtracking.
Remove the ? resolves the issue.
I also remove the redundant escape of . inside character class, and changed the regex a bit.
^\w+([.-]\w+)*#\w+([.-]\w+)*\.\w{2,3}$
Do note that many new generic TLDs have more than 3 characters. Even some of the gTLD before the expansion have more than 3 characters, such as .info.
And as it is, the regex also doesn't support internationalized domain name.

Regex in JavaScript

Suppose we don't know how many slashes we could get in a string but we do not want any extra slashes. So if we get this string '/hello/world///////how/are/you//////////////' we should transform it to the form of '/hello/world/how/are/you/'. How to do it with the help of regular expressions in JavaScript?

"/hello/world///////how/are/you//////////////".replace(/\/+/g, "/")

'/hello/world///////how/are/you//////////////'.replace(/\/{2,}/g, '/');
This might be an incy wincy bit faster than mkoryak's suggestion, for it will only replace where necessary – i.e., where there's multiple instances of /. I'm sure someone with a better understanding of the nuts and bolts of the JavaScript regular expression engine can weigh in on this one.
UPDATE: I have now profiled mine and mkoryak's solutions using the above string but duplicated hundreds of times, and I can confirm that my solution consistently worked out several milliseconds faster.

Edited: mkoryak's answer below is way better. Leaving this in case the info it contains is useful for someone else.
You could capture each word + slash group and look ahead (but don't capture) for one or more extra slash. Like...
(\w+\/)(?:\/)*(\w+\/)(?:\/)*
First () captures one or more of any word character followed by a slash, second () looks for a slash but doesn't capture, * means find 0 or more of the proceeding token. Etc.
Hope that helps!

I want to make a regex for string which matches from point A till point B
text= "testtttExecuted 'show bootvar' on \n10.238.196.66. kjdkhfkh Executed tsttt\n fhgkhkh"
Output should be
testtttExecuted 'show bootvar' on \n10.238.196.66. kjdkhfkh
I want to make a regex for string which matches from point A till point B
text= "testtttExecuted 'show bootvar' on \n10.238.196.66. kjdkhfkh Executed tsttt\n fhgkhkh"
Output should be
testttt<font color='red'>Executed 'show bootvar' on \n</font>10.238.196.66. kjdkhfkh <font color='red'>Executed tsttt\n</font> fhgkhkh

How to search csv string and return a match by using a Javascript regex

I'm trying to extract the first user-right from semicolon separated string which matches a pattern.
Users rights are stored in format:
LAA;LA_1;LA_2;LE_3;
String is empty if user does not have any rights.
My best solution so far is to use the following regex in regex.replace statement:
.*?;(LA_[^;]*)?.*
(The question mark at the end of group is for the purpose of matching the whole line in case user has not the right and replace it with empty string to signal that she doesn't have it.)
However, it doesn't work correctly in case the searched right is in the first position:
LA_1;LA_2;LE_3;
It is easy to fix it by just adding a semicolon at the beginning of line before regex replace but my question is, why doesn't the following regex match it?
.*?(?:(?:^|;)(LA_[^;]*))?.*
I have tried numerous other regular expressions to find the solution but so far without success.

I am not sure I get your question right, but in regards to the regular expressions you are using, you are overcomplicating them for no clear reason (at least not to me). You might want something like:
function getFirstRight(rights) {
var m = rights.match(/(^|;)(LA_[^;]*)/)
return m ? m[2] : "";
}

You could just split the string first:
function getFirstRight(rights)
{
return rights.split(";",1)[0] || "";
}

To answer the specific question "why doesn't the following regex match it?", one problem is the mix of this at the beginning:
.*?
eventually followed by:
^|;
Which might be like saying, skip over any extra characters until you reach either the start or a semicolon. But you can't skip over anything and then later arrive at the start (unless it involves newlines in a multiline string).
Something like this works:
.*?(\bLA_[^;]).*
Meaning, skip over characters until a word boundary followed by "LA_".