Regex - Output character not valid

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I'm trying to create a function to check if a field is valid based on a set of characters and, if not, output which ones are not allowed. Don't know if it is the best approach, but basically instead of telling the user which ones he can use, I want to tell which ones he can't.

function allowedString(field){
    var validCharacters = new RegExp('^[a-zA-Z0-9áéíóúÁÉÍÓÚñÑ_-¿?¡!.,;:$() ]*$');
    if(!validCharacters.test(field.val())){
        var invalid = ?;
        return "Invalid characters: "+invalid;
    }
}

Using your character set in your regex, you can remove all those characters from the string and resultant will be the non-allowed characters. Try this JS codes,

function allowedString(s){
    var validCharacters = new RegExp('^[a-zA-Z0-9áéíóúÁÉÍÓÚñÑ_-¿?¡!.,;:$() ]*$');
    if(!validCharacters.test(s)){
        var invalid = s.replace(/[a-zA-Z0-9áéíóúÁÉÍÓÚñÑ_-¿?¡!.,;:$() ]*/g,'');
        return "Invalid characters: "+invalid;
    } else {
        return "All characters are valid"; // return any message you want
    }

}


console.log(allowedString('aa@@bb##'));
console.log(allowedString('abc'));
console.log(allowedString('aa@@bb##~~^^'));

How to: Strip Invalid Characters from a String, Read an example that shows how to strip potentially harmful characters from a string by using the static Regex.Replace method. Output: 9925612824 is a valid mobile number. 8238783138 is a valid mobile number. 02812451830 is not a valid mobile number. Example 2: Below example demonstrate the use of regex in Email ID Verification.

You can split the string and deal with it as with an array (not sure about the performance, though).

function allowedString(field){
    const validCharacters = new RegExp('^[a-zA-Z0-9áéíóúÁÉÍÓÚñÑ_-¿?¡!.,;:$() ]*$');
    const disallowed = field.val().split('').filter(x => !validCharacters.test(x));

    if (disallowed.length) {
        return disallowed.join('');
    }
}

Regex.IsMatch Method (System.Text.RegularExpressions , Indicates whether the regular expression finds a match in the input string. The first set, which contains four characters, must consist of an alphanumeric RegularExpressions; public class Example { public static void Main() { string[] The example displays the following output: // 1298-673-4192 is a valid part number. A -in a character class surrounded on both sides is a regex meta character to to detect a valid regular expression? an output of SHA-1 with first 2-bit are

I'd reverse the test: Is there an invalid character within the string?

Take care you have to escape the dash in a character class except in first and last position.

function allowedString(field){
    var invalidCharacters =/([^a-zA-Z0-9áéíóúÁÉÍÓÚñÑ_\-¿?¡!.,;:$() ])/;
    invalid = invalidCharacters.exec(field);
    if (invalid != null) {
        return "Invalid characters: "+invalid[1];
    } else {
        return "OK";
    }
}
console.log(allowedString('abc'));
console.log(allowedString('abc@def'));
console.log(allowedString('abc§def'));

Everything you need to know about Regular Expressions, Whenever you want to check whether a string is a valid zip code, you can match it Most characters in a regex pattern do not have a special meaning, they Regular expressions are useful in search and replace operations. Approach: The idea is to use Regular Expressions to validate if the given username is valid or not. The following steps can be followed to compute the answer: Get the string. Form a regular expression to validate the given string. According to the conditions, the regular expression can be formed in the following way: regex = "^[aA-zZ]\\w{5, 29}$"

[PDF] Regular Expressions: The Complete Tutorial, Specialized Tools and Utilities for Working with Regular Expressions . This tutorial is quite unique because it not only explains the regex syntax, but also A "match" is the piece of text, or sequence of bytes or characters that pattern Replace method will remove the regex match from the string, and insert the replacement. I need a regex to match if anywhere in a sentence there is NOT either < or >. If either < or > are in the string then it must return false. I had a partial success with this but only if my

Regular expressions, Regular expressions are patterns used to match character and test() methods of RegExp, and with the match(), matchAll(), replace(), If the number is invalid, the script informs the user that the phone number is not valid. So when I try and create a RegEx for invalid characters I have this, [^a-zA-Z0-9 ]. Then I have strings that I want to search based on the RegEx and when it finds an invalid character, it checks if the character before it is invalid. for example, "test test +?test" So what I want to happen is if there are two invalid characters, one after the

For example, consider a very commonly used but extremely problematic regular expression for validating the alias of an email address. The regular expression ^[0-9A-Z]([-.\w]*[0-9A-Z])*$ is written to process what is considered to be a valid email address, which consists of an alphanumeric character, followed by zero or more characters that can be alphanumeric, periods, or hyphens.

Comments
  • You have ; following the parenthesis not sure if that should be there
  • You could iterate through the String, and get each character which fails the regexp
  • The ; is allowed, that why I included it. About iterating the string, would that actually be a good approach? (thinking about performance on long strings)
  • You might be able to do a string.replace, and replace your regexp with '', then if the String is not empty, print the string, otherwise if it's empty the regexp passed
  • This function is passed once the required function was true. So some string is needed.
  • For some reason returns ".replace is not a function" when it shouldn't
  • @RGC: You need to use replace on string where as you might be using on field. Can you try doing field.val().replace(/[a-zA-Z0-9áéíóúÁÉÍÓÚñÑ_-¿?¡!.,;:$() ]*/g,'');
  • You are right, I missed .val() Then, wouldn't it be the same to do if(invalid !== "")? Works when wrong, but when string is right return Invalid character: I tried this, and it's ok for some like "#" but with "{" return ok..
  • Because I use it to tell the user which characters cannot use. By adding that, if the user types "#" or "####" I just tell him he cannot use the character "#".
  • Thanks lot mate!!