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HTML Form Validation - Check for Specific Characters

I'm using the Html5 pattern to validate my inputs on forms. I need to make sure an input has the following rules:
A maximum and minimum of 8 characters
The first 3 must be the specific letters wrx (lowercase)
The last 5 must be numbers.
Eg. wrx12345
Can I even do this with pattern or do I need to use JavaScript?

I believe the regex pattern you are looking for is /^wrx[0-9]{5}$/. A visual representation of this here:
And implemented in html:
<input name="example" pattern="^wrx[0-9]{5}$">

You can use regex in Javascript with this regex:
"/[wrz][\d]{5}/g".
To test the minimum = maximum length = 8, you can just test it in javascript.
If the length egual 8, use the regex
Else, show error
I think this could work

You don't need Javascript to do this.
The pattern attribute uses regular expressions so you can use something like this: ^wrx[0-9]{5}$
The ^ and $ indicates the start and end of the string. Then 'wrx' has to be matched exactly and [0-9]{5} looks for 5 number bewteen 0-9.
You can use something like RegExr to test your patterns.

Pattern for form input field validation

I have following scenario, I have to validate the form input field whose first character can be either P or B or R, the second character can only be C and after that 6 digits. I was using this pattern:
pattern="^[PBR]C\d{6,6}$"
Now I have to add one more condition to the input field to allow input of the form BRC100101, so now the input can also start from BR, then letter C and then 6 digits. I tried the below pattern, but couldn't quite get what I'm looking for.
pattern="^(P)(B)(R)(BR)C\d{6,6}$"

Least amount of characters and more professional.
([PBR]|BR)C\d{6}
This way is little easier to read/understand, readability goes a long way.
(P|B|R|BR)C\d{6}
I'm not a regular expresssion expert, I usually use regexr.com to help me build and test the expressions I use in my code.
http://regexr.com/
Demo:
http://regexr.com/3ggi6

You can try this way,
([PBR]|BR)C\d{6,6}
Live Demo: https://regex101.com/r/RN86w1/2

You can try
([PBR]|BR)C\d{6}
Demo https://regex101.com/r/SDgguC/1

How to get the valid part of a regex match

I want to test if a user string is "ok so far", in that it might not be valid as a whole but it is a subset of a valid one.
I have a regex say ^[0-9]{4}-[0-9]{4}-[0-9]{4}-[0-9]$
such that "1234-1234-5678-5678" is valid
"1234-12" or even "1" does not match pattern but its a valid subset of a valid format, in other words the input is ok so far.
is there a neat way of doing this without making many many regexes, its friday.

Not sure if I understood well your problem, but I think you want to have something like this:
^([0-9]{4}-){1,3}[0-9]{1,4}$
Working demo
This will match set of 4 digits and can have the last set from 1 to 4 digits
You can also shorten your regex with:
^(\d{4}-){1,3}\d{1,4}$

You could possibly use one final regex for validation of the form you currently have, and a on the fly regex for the user input being valid for each subset.
My idea would be to have ([0-9]{1,4}-)+

For your case this will check as one types:
/^(\d(\d(\d(\d(-(\d(\d(\d(\d(-(\d(\d(\d(\d(-(\d)?)?)?)?)?)?)?)?)?)?)?)?)?)?)?)?$/

This regex will match key for key as you type, although it is a little cumbersome.
^([0-9]{1,4}|[0-9]{4}-[0-9]{0,4}|[0-9]{4}-[0-9]{4}-[0-9]{0,4}|[0-9]{4}-[0-9]{4}-[0-9]{4}-[0-9]{0,4})$
Here is a live example

Regex Comma Separated Phone Number

I am trying to generate a regex which would match the following sequence-
+91123456789,+41123456789,+21123456789.... and so on, there is no limit of phone numbers.
Basically the usage is to validate the phone numbers which users may add, phone number can be multiple and need to be separated by commas, I am already removing the empty spaces which users may add, so no worry for that.
I am not good with regex and have created the following regex but it doesn't matches the preceding phone numbers, means the whole string of phone numbers do not match-
^\+?\d{1,4}?[-.\s]?\(?\d{1,3}?\)?[-.\s]?\d{1,4}[-.\s]?\d{1,4}[-.\s]?\d{1,9},\+?\d{1,4}?[-.\s]?\(?\d{1,3}?\)?[-.\s]?\d{1,4}[-.\s]?\d{1,4}[-.\s]?\d{1,9}$
I need to validate the user input using javascript or jquery.
Valid Phone number should be having country code like +91 or +21 etc country code can be of one or two digits, then the number of digits need to be 7 to 9.
I anyone could help, it would be highly appreciable, I have spent lot of time on this one.

To validate the whole string handling mulitple values sepparated by comma just add an group with * multiplier:
^\+\d{8,11}(,\+\d{8,11})*$

If I understand the requirements correctly, the following regex should work
\+\d{9,11}
However, you can separate the country code out, for if you need to allow for (+44)xxxxxxxxx
\+\d{2}\d{7,9}
if the requirement is to allow for 1 country code as well, adjust the regex to the following
\+\d{1,2}\d{7,10} //I think to 10, not sure on their numbers
You can update the ranges as you see fit :)
Demo: https://regex101.com/r/rJ4wM7/1

restrict characters in form field

I've an HTML field in a form and, using JS and Regex, I must restrict the characters the user can insert in the field. The user of the form can only insert the following characters ( ) * + ^ / X x, and numbers and spaces (when he digits or pastes a different character nothing is written). Is this possible? I need the Regex, I eventually know how to do with JS.

Try this regex
[^\(\)\*+\^/Xx0-9 ]
Here we are trying to find a pattern which contains none of the allowed characters. If you find it this means that the character entered was wrong.

There is no right or wrong answer to this.
Usually it is less expensive to check using the bias of the logic for the particular condition.
If it sounds better saying whats allowed, then use the allowed (positive) character class.
Allowed class: [()*+^/Xx0-9 ], Checks: <space> (-+ /-9 X \^ x
Not allowed class: [^()*+^/Xx0-9 ], Checks: \0-\37 !-' , \- . :-W Y-\] _-w y-\377
Statistically, if %99 of the data enterred were valid, the 'Allowed' class would do less work in that
not every character or range has to be checked.
Where the 'Not-Allowed' class will have to check every range.
In this particular case, the negative class has many more ranges and characters to check, its borderline
more efficient if most of the data were invalid,

With regard to:
[^\(\)\*+\^/Xx0-9 ]
None of those characters need to be escaped inside a set (but it is okay to do so).
If you want to restrict as the user types (this uses jquery methods):
$('#in1').keyup(function (evt) {
var content = $('#in1').val();
$('#in1').val(content.replace(/[^()*+^/Xx0-9]/g, ""));
return true;
});
Where 'in1' is the id of the input.